In November I heard from Stefan who had installed Windows on his M350C:
I'm not a Windows expert and on the rare occasions I do use it it is usually in the form of Windows 7. This time I decided to install Windows 10 and found it to be ultra easy to do.
Having done the basic install of Windows 10 the M350C specific drivers can be found on AMD's website at Ryzen Embedded R1000 Series Drivers & Support. Just install the two packages: 'AMD Embedded Windows Chipset drivers' to deal with most of the unrecognised devices and 'AMD Embedded Windows 64-bit Catalyst Driver' for the GPU. They do list drivers for both Window 10 and Windows 11.
I must say for 10W-Max devices it's very usable in Windows 10. It doesn't have TPM 2.0 (as for example Futro S940 with its Intel J5005 SoC), but probably it will run Windows 11 as well with the TPM bypass trick during the installation: