For anyone running a ROM based very closely on AOSP, the ability to disable Fast Pair was sadly not built into the OS until Android 14
Before Android 14, it is possible that Google has backported this setting to your device using Play Services. It can be found under Google Settings, Devices and sharing, Devices, and "Show Notifications"
NVidia and Linux... don't get along very well. They've also been caught violating the GPL in their drivers, resulting in the kernel being hardcoded to block them in some instances. There is good reason why Valve picked an AMD APU in their handheld
Modern bluetooth controllers store the paired devices on their onboard memory, rather than only in the OS (allowing your bluetooth peripherals to work in the BIOS etc). If the two paired device lists fall out of sync, this could lead to erroneous behavior, especially since you're dual booting two completely different operating systems using completely different driver implementations to talk to your hardware
Just wanted to share why things are broken - not trying to persuade you to change your workflow. Use whatever works best for you!