@larrylf Well, the extra logging didn't help, but after a lot of googling, and some playing around, I got it to work.
In case someone else runs into this issue, here is what I had to do:
(Connect via cable, ssh to the pi)

pi@duet3:~ $ sudo wpa_passphrase

type in your ssid and password. It will generate a long string.

pi@duet3:~ $ sudo nano /etc/wpa_supplicant/wpa_supplicate.conf

You will see your password in the clear here:

network={
    ssid="myssid"
    psk="my password"
}

delete your your password, and replace with the generated string from above:

network={
    ssid="myssid"
    psk=415e02a3e30be000b075c2ea320327300f7ba73f9fb12347247b233e52babcd5
}

(Notice it is not in quotes)
save, and exit
Now, edit /etc/network/interfaces, and add these lines:

allow-hotplug wlan0

iface wlan0 inet dhcp
	wpa-ssid myssid
	wpa-psk 415e02a3e30be000b075c2ea320327300f7ba73f9fb12347247b233e52babcd5

(again - no quotes) Save, and exit.

Reboot (ok, you can probably just resart things, but rebooting works for sure).

I find that the UI on my SBC still shows an icon saying that wifi is not connected, but I can still access DWC from my browser now, over wifi.

@larrylf Well, the extra logging didn't help, but after a lot of googling, and some playing around, I got it to work.
In case someone else runs into this issue, here is what I had to do:
(Connect via cable, ssh to the pi)

pi@duet3:~ $ sudo wpa_passphrase

type in your ssid and password. It will generate a long string.

pi@duet3:~ $ sudo nano /etc/wpa_supplicant/wpa_supplicate.conf

You will see your password in the clear here:

network={
    ssid="myssid"
    psk="my password"
}

delete your your password, and replace with the generated string from above:

network={
    ssid="myssid"
    psk=415e02a3e30be000b075c2ea320327300f7ba73f9fb12347247b233e52babcd5
}

(Notice it is not in quotes)
save, and exit
Now, edit /etc/network/interfaces, and add these lines:

allow-hotplug wlan0

iface wlan0 inet dhcp
	wpa-ssid myssid
	wpa-psk 415e02a3e30be000b075c2ea320327300f7ba73f9fb12347247b233e52babcd5

(again - no quotes) Save, and exit.

Reboot (ok, you can probably just resart things, but rebooting works for sure).

I find that the UI on my SBC still shows an icon saying that wifi is not connected, but I can still access DWC from my browser now, over wifi.

@phaedrux will do, thanks.

@phaedrux Wifi router is about 30' away, on a lower floor. The signal shows a strong on other devices. I have several wifi devices in the room, and none have problems connecting.
Also, the behavior I'm seeing with ssh make me thing its not a device problem, but something in the DWC SW (when wifi itself finally does show up, the dwc console shows immediately, but then fails to connect - not sure if this means connect with the duet (I never see this error on the Pi screen), or some other connection ig going on after the initial html layout,

M122:
m122
=== Diagnostics ===
RepRapFirmware for Duet 3 Mini 5+ version 3.4.1 (2022-06-01 21:06:56) running on Duet 3 Mini5plus WiFi (SBC mode)
Board ID: P76RB-H396U-D65J0-40KM8-ML03Z-Z7HZZ
Used output buffers: 1 of 40 (12 max)
=== RTOS ===
Static ram: 103684
Dynamic ram: 99256 of which 0 recycled
Never used RAM 38772, free system stack 206 words
Tasks: SBC(ready,2.1%,452) HEAT(notifyWait,0.1%,358) Move(notifyWait,0.0%,363) CanReceiv(notifyWait,0.0%,942) CanSender(notifyWait,0.0%,372) CanClock(delaying,0.0%,339) TMC(notifyWait,0.7%,114) MAIN(running,95.0%,558) IDLE(ready,1.4%,29) AIN(delaying,0.8%,273), total 100.0%
Owned mutexes: HTTP(MAIN)
=== Platform ===
Last reset 00:01:42 ago, cause: power up
Last software reset at 2022-07-24 13:48, reason: User, GCodes spinning, available RAM 38696, slot 2
Software reset code 0x0003 HFSR 0x00000000 CFSR 0x00000000 ICSR 0x00000000 BFAR 0xe000ed38 SP 0x00000000 Task SBC Freestk 0 n/a
Error status: 0x00
MCU revision 3, ADC conversions started 102555, completed 102555, timed out 0, errs 0
Step timer max interval 1490
MCU temperature: min 21.6, current 27.1, max 27.3
Supply voltage: min 24.1, current 24.1, max 24.2, under voltage events: 0, over voltage events: 0, power good: yes
Heap OK, handles allocated/used 0/0, heap memory allocated/used/recyclable 0/0/0, gc cycles 0
Events: 1 queued, 1 completed
Driver 0: standstill, SG min 0, read errors 0, write errors 0, ifcnt 11, reads 5370, writes 11, timeouts 0, DMA errors 0, CC errors 0
Driver 1: standstill, SG min 0, read errors 0, write errors 0, ifcnt 11, reads 5370, writes 11, timeouts 0, DMA errors 0, CC errors 0
Driver 2: standstill, SG min 0, read errors 0, write errors 0, ifcnt 11, reads 5369, writes 11, timeouts 0, DMA errors 0, CC errors 0
Driver 3: standstill, SG min 0, read errors 0, write errors 0, ifcnt 11, reads 5369, writes 11, timeouts 0, DMA errors 0, CC errors 0
Driver 4: standstill, SG min 0, read errors 0, write errors 0, ifcnt 11, reads 5370, writes 11, timeouts 0, DMA errors 0, CC errors 0
Driver 5: not present
Driver 6: not present
Date/time: 2022-07-26 04:49:59
Cache data hit count 237203523
Slowest loop: 56.38ms; fastest: 0.10ms
=== Storage ===
Free file entries: 10
SD card 0 not detected, interface speed: 0.0MBytes/sec
SD card longest read time 0.0ms, write time 0.0ms, max retries 0
=== Move ===
DMs created 83, segments created 0, maxWait 0ms, bed compensation in use: none, comp offset 0.000
=== MainDDARing ===
Scheduled moves 0, completed 0, hiccups 0, stepErrors 0, LaErrors 0, Underruns [0, 0, 0], CDDA state -1
=== AuxDDARing ===
Scheduled moves 0, completed 0, hiccups 0, stepErrors 0, LaErrors 0, Underruns [0, 0, 0], CDDA state -1
=== Heat ===
Bed heaters 0 -1 -1 -1, chamber heaters -1 -1 -1 -1, ordering errs 0
=== GCodes ===
Segments left: 0
Movement lock held by null
HTTP* is doing "M122" in state(s) 0
Telnet is idle in state(s) 0
File is idle in state(s) 0
USB is idle in state(s) 0
Aux is idle in state(s) 0
Trigger* is idle in state(s) 0
Queue is idle in state(s) 0
LCD is idle in state(s) 0
SBC is idle in state(s) 0
Daemon is idle in state(s) 0
Aux2 is idle in state(s) 0
Autopause is idle in state(s) 0
Code queue is empty
=== CAN ===
Messages queued 829, received 0, lost 0, boc 0
Longest wait 0ms for reply type 0, peak Tx sync delay 0, free buffers 18 (min 18), ts 512/0/0
Tx timeouts 0,0,511,0,0,316 last cancelled message type 30 dest 127
=== SBC interface ===
Transfer state: 5, failed transfers: 0, checksum errors: 0
RX/TX seq numbers: 4393/4393
SPI underruns 0, overruns 0
State: 5, disconnects: 0, timeouts: 0 total, 0 by SBC, IAP RAM available 0x0f1ec
Buffer RX/TX: 0/0-0, open files: 0
=== Duet Control Server ===
Duet Control Server v3.4.1
Code buffer space: 4096
Configured SPI speed: 8000000Hz, TfrRdy pin glitches: 0
Full transfers per second: 0.03, max time between full transfers: 110.9ms, max pin wait times: 69.5ms/10.5ms
Codes per second: 0.00
Maximum length of RX/TX data transfers: 3244/804

@o_lampe No, I am using the Pi as an SBC

I have a Duet 3 mini 5+, with Rasp Pi (3B+) & display.
I am having some odd issues connecting:

1. When I power on, the WiFi generally remains 'unassociated'. I can leave it for an hours, and wifi doesn't connect. Then, If I plug in a cable, and open SSH, do a 'ifconfig' I see wifi is up (then all the sudden I can use wifi)
2. When I connect - via cable or wifi, I will immediately see the DWC layout, then a diag saying 'Connecting...' - this almost always times out, and I get an error that http isn't working.

Mind you, this is frequent, and random, but I do occasionally connect, and have been able to commision my printer - so yes, wifi is configured correctly.
When I booted the Pi, I did an apt update / upgrade, so I should have the latest of everything.

I would really like networking to be more reliable - any ideas?

@droftarts yes, the thermistor was a mistake - in fact, I seem to have the wrong sensors everwhere (PT100's in the mainboard TEMP, thermistor in the daughterboard).
Fixed now, but frustrating...

@larrylf yes, that worked - thank you

@dc42 Oh, so you're saying that I have to identify it as the board, not what its used for?
I'll try to find what it should be, then

@phaedrux Sorry, it is the PT100 board, and I am using a thermistor in it.

I'm in the process of setting up a printer with a duet3 mini 5+. I have the temperature daughterboard for it, and am tried to set it up in my config file.
From the documentation, it looks like I should use M308:
M308 S3 Y"thermistor" P"spi.cs1" T100000 B4138

But when it boots up, I get an error "pin spi.cs1 doesn't support analog input"
What am I doing wrong?