Hello! This sounds like it could be a software-based issue, since I believe the UI error code is related to One UI, Samsung’s home launcher. There could be a few ways to fix this issue.
1: Factory reset from recovery. Since you can’t get to the settings (since it keep crashing), you can try to factory reset. THIS WILL REMOVE ALL DATA FROM THE PHONE, and you will need your google account info to get back into the phone afterwards, so be sure to have that on hand.
First, turn the phone off (or let it die and then charge it), and then hold down the volume up key, menu/bixby (I can’t remember if the A30 has either of these, so if it doesn’t you don’t need to worry about it) and the power.
Keep holding until you get to the first splash screen (it’ll say Samsung on it). After that it should take you to another Menu with a bunch of options (you use the volume buttons to go up/down, power button to select).
From there, you go to “Factory reset” and select it. Give it about ten seconds to wipe and then hit restart. From there it’ll boot and bring you to the setup screen. It’ll be like you have a brand new phone!
2: Flashing. This method is a bit trickier, since it involves reflashing software. I can walk you through this, but it would involve downloading some additional software, and the firmware for the phone. THIS ALSO DELETES EVERYTHING ON THE PHONE, so make sure you have your google account info as well.
Hope this helps! 😊