Secure boot must have all kernel modules signed. The system that Fedora uses is a way that builds the drivers from source with every new kernel update. It works, but it can't be modified further.

The primary issue you will likely come across is that the nvcc compiler is not open source and it is part of the CUDA chain. You can't build things like lama.cpp without nvcc and have CUDA support. Most example type projects have the same issues. Without nvcc fully open, you are still somewhat limited. Also the toolchain for nvcc screws up the open source built stuff and will put you back at the train wreck of secure boot. If Nvidia had half a working brain, they would open source everything instead of the petty conservative nonsense stupidity that drives proprietary fools. There is absolutely no room in AI for anyone that lacks full transparency.

The opensource drivers are not included by default (out of tree) so no this is the same scenario.

If the boot files change, you cant just fix the signature. Thats a key feature of public-private-cryptography

This is entirely plausible, but I don’t know if it’s there yet. I’ve long since moved to AMD GPUs so I can’t really fiddle and find out. Give the open source drivers some time to mature.

Until then, you are reasonably safe running Linux with secure boot turned off. I’m no expert on the matter, but I’m not familiar with any ongoing threats to boot loader in Linux distributions. Stick to your official repos to be safest, unverified user maintained sources like AUR and COPR are possibly more likely to harbor security threats, don’t use them if you don’t need to or don’t know what you’re doing. Password your bios and require a password to log in to your operating system. Common sense is a better defense than secure boot.