I added a new pc to syncthing this week, I installed it and scanned a qr and was done in like three minutes.

If you want to register a laptop with the apple business manager you have to use the configurator mobile app, so not even having another apple pc is sufficient, to set up a mobile device you have to use the configurator desktop app.

https://support.apple.com/guide/apple-business-manager/add-devices-from-apple-configurator-axm200a54d59/web