

Stuff like PostmarketOS looks interesting. The new Furilabs phone doesn’t sound too bad either.
If you have the money, consider donating $5 to a couple Linux mobile projects. Small donations here and there can be the difference needed to make Linux mobile a viable option.
My method is much more manual and involved, but fits my needs:
I have my pictures, documents, and music folders synced automatically to a few computers via Syncthing. At the start op each month, I export my contacts, Obtainium apps, and other files to my documents. At this time, I also make backups to the cloud and make a couple copies to external hard drives. It may sound intensive, but it only takes 5 minutes a month.
I restart / update my phone very often for various tests and projects. Whenever I need to do so, I upload these files from my computer or hard drive. Using a guide that I’ve made myself, it takes maybe ten minutes to have my phone exactly the way it was before.