@800XL I think guides even aren’t needed) Before flashing Pixel 3a with UT, you will need to flash it to Android 9. The easiest way is doing it via Google’s web-based flasher, you don’t even need to download firmware to your PC. This flasher will download selected firmware automatically and will unlock bootloader also automatically… or at least semi-automatically, you will still need to follow some steps that is displayed on your PC’s screen (not phone’ screen!).
Check UT site for firmware code
@800XL I’m afraid, yes. You can try but there is no guarantees that it is possible at all. I have checked it across some forums and looks like it’s pretty uncommon situation when Pixels are locked. Anyway, Pixel 3a is pretty cheap today (I’ve bought one in less than $100 with ideal condition) so if you have the version with encrypted bootloader, you can try to sell your current model and buy a new one without encrypted bootloader (probably it may cost a little more if you search specifically 🤷♂️)
