Need help with android cell phone [View all]

I need to finally do a thorough review and cleanup of my phone(s).

What precipitated this was that an app that came with the phone (Gallery, for viewing/managing media) did an auto update (which I usually do not allow, but this slipped through) and now the updated version is a 14-day trial of their Pro version! (Grrrrrrr!) Usually "uninstall" rolls back just the update(s) to the factory version, but not this time, nope, you can't do that.

I need an in-depth understanding of how backups work. The one time, years ago, when I thought I had my phone backed up sufficiently and correctly and so did a factory reset, I lost tons of stuff.

I want to be able to micromanage this process so that does not happen again.

Can anyone provide some guidance on this journey? I'm fairly tech savvy, but have just not kept up in the past few years. Thanks to anyone who can help.