I updated a TC77 with the lifeguard U138 patch for Android 10.

1- After it applied the update, the device is doing boot loop. I had to simultaneously press and hold the Power Button + Scanner Trigger + PTT button  to leave it, and I had fastboot screen.

2- To leave this fastboot mode, i had to simultaneously press and hold the Power Button + Scanner Trigger + sound down button to leave.

After reboot, it it is asking for the password for android. These devices were never setup with a passcode or password.