Sounds like you aren't using the full zip file releases.

If you still have access to DWC. Upload these zip files, one at a time in the system tab. Don't extract them first. Reboot after each. Use M115 in the gcode console to verify the firmware has been applied.
https://github.com/Duet3D/RepRapFirmware/releases/download/2.05.1/Duet2Firmware-2.05.1.zip
https://github.com/Duet3D/RepRapFirmware/releases/download/3.0/Duet2and3Firmware-3.0.zip
https://github.com/Duet3D/RepRapFirmware/releases/download/3.3/Duet2and3Firmware-3.3.zip
https://github.com/Duet3D/RepRapFirmware/releases/download/3.4.6/Duet2and3Firmware-3.4.6.zip