Hi
This is a topic near to my heart. I found this explanation very lucid and works perfectly. It virtually covers every eventuality - uefi boot, bios boot, whatever you care to throw at it.
https://forums.linuxmint.com/viewtopic.php?t=287353
I know it sounds a little weird but I run mint from a 128gb usb3 flashdrive all the time. I travel between two countries very regularly, keep all my documents in the cloud (I’m a huge fan of insync) and have every app you could ever want installed and configured. Yes I appreciate that a flash drive can fail and so I keep a backup using timeshift ready to go if needed. My experience over the last three years shows that a failure is pretty unlikely.