I've been dual-booting Windows 11 and LMDE for a few months now on seperate drives. I've got secure boot enabled and have a Nvidia GPU. I've only had to go on Windows once to play a game from the Xbox app(I still have an active gamepads subscription) with my friends online.
It's been working fine for the most part. I haven't been able to get a second monitor to work properly again after disabling it in nvidia-settings shortly after installation. This has been a minor annoyance that I'm sure I could figure out with some effort.
Did you generate keys? Or use keys already on the system? Also, is this Mint 20?