If that's the case, then you should answer the OP with how it's set up. OP is specifically asking how to do it with random drives other people hands them, not trusted drives always connected.
What is the disaster that could happen you’re referring to?
Auto mounting random USB sticks has never been wise. No telling what random malware they contain.
Just to clarify. In-kernel drivers is not the same as open source firmware. Most bluetooth dongles use the in-kernel driver, but require proprietary firmware to be loaded before they work. Most of that firmware is present in the linux-firmware packages/repository, but the setup would no longer be FOSS only.