@Timothee-Leblond If the RPi can connect to the network/internet, I'd guess that there is something stopping incoming connections to the RPi, possibly blocked at the router. Check with your IT department.
Another way to test would be to set the RPi in access point mode, which you can also do with the Mini 5+ in standalone mode. See https://docs.duet3d.com/en/User_manual/Reference/Gcodes#m589-configure-access-point-parameters
Then your PC can connect directly to the WiFi network that creates.
Ian