I have no clue yet if an open source solution exists, but I’m just getting started volunteering with a local animal rescue, and they definitely need a better solution for records management.

Looks like this is a list of manufacturers that allow bootloader unlocking. If you want to install a custom ROM, you first need to unlock the bootloader. Note that carrier branded devices of these brands may still have a locked bootloader. The example I’m most familiar with is the Verizon version of Pixels… I always by the carrier unlocked version of the Pixel to ensure an unlocked bootloader.