I’ve gotten the BraX3 caught in a bootloop several times after flashing in fastboot mode and found that it can be powered off when it does this by holding in the power button for a long time…even after it looks like the screen is blank. I’d say hold that power button for about 30 seconds to make it really power down and not start a bootloop again!
I hope that works for u! SPFlash always works with Lunar OS and makes things easy…if u have LInux I got it to work that way and wrote about if u search. I’m not sure if flashing is something u are comfortable with. The problems I had with that program were always when Ubuntu Touch was on the phone which doesn’t sound like that’s your case.
Try to flash Lunar OS on it!