Reverting on Pixel Tab

sudo systemctl stop fwupd.service then boot into bootloader:

You need to boot your device into the bootloader interface. To do this, you need to hold the volume down button while the device boots. The easiest approach is to reboot the device and begin holding the volume down button until it boots up into the bootloader interface.

Open https://flash.android.com/back-to-public, on Brave disable shields and the device must appear and flash with latest public OS release.

Ref: https://grapheneos.org/install/web#prerequisites

There is also a repair tool: https://pixelrepair.withgoogle.com/

Instructions for adb sideload: https://android.stackexchange.com/questions/230999/enable-usb-debugging-through-recovery-mode-and-adb-sideload

“No command” screen to menu: https://www.reddit.com/r/AndroidQuestions/comments/uujah0/trying_to_use_recovery_mode_and_shows_no_command/

Flash with command line flashboot tool: https://source.android.com/docs/setup/test/running