I was wondering if sending my MacBook Pro to an unfamiliar computer store for repairs would put my data at danger of theft or leakage. FileVault is activated, of course, and my password is strong. I'm not clear of the mechanics of how data leaks happen during computer repairs, but I continue to read about them. Although I have a complete Time Machine backup, ideally I would not need to wipe and restore. If it matters, it's a display repair for a 15-inch 2018 MacBook Pro.
Generally speaking, a standard repair store will not ask for any password to proceed with the external display repair, you shouldn't and wouldn't give any password or user account to them at all. Just keep your Mac powered off completely and send it to the display repair.
Yet if you need any software repair, you should erase your Mac or they have access to your files and documents!