You could install another operating system on the phone. For example, as far as I know GrapheneOS (https://grapheneos.org) still has limited support for the Pixel 4a and apparantly does not include the new changes google introduced at this time (there are already a few threads about this in the GrapheneOS forums).

There is probably a Hackerspace or a Makerspace somewhere around and it's very likely that you will find people there who will help you with working on making your device usable again and with backing up your data.