I have moved over to using UT on a pixel 3a as my main phone. I have come across a few issues.
The automatic brightness does not work at all. You can enable or disable it from the menu but nothing. You can manually adjust it fine but it won't automatically adjust itself. In terms of Bluetooth, I have across some items that don't want to connect. A Bose speaker I have will connect but drop off and the bose speaker dosen't akowledge the connection at all. Generally you connect a new device and the speaker will state it has a new device connected and say its name.