I did it a little different. As I wanted to keep everything already on my phone, I didn’t even consider switching back to Fairphone OS first. Although in the offical guide no data loss is mentioned, it seemd to risky for me. Apart from this, Fairphone doesn’t offer Android 12 (S) for the FP3. I just upgraded to /e/s S dev OVER Q dev, thanks to the lead and encouragement from the community.
- Turn on USB-Debugging in the developer options on your phone.
- Reboot to /e/s’ Recovery Mode
- Choose “Apply Update”, then “Apply from ADB”
adb sideload /path/to/zip (inserting the path to your /e/OS package) on your computer
- Reboot your phone and you are done.
Everything worked out smooth for me, nevertheless it might be risky. I just went all in, eyes closed. I hadn’t any data loss and everything (apps & data) was kept in place. Insofar as Androids architecture changes, that might not be the case with future versions (Android 13+). For posibilities of data backup, you can look up the dicussion I had that led me to my upgrade here. You should also keep in mind that, for reasons unknown to me, an upgrade from a dev build to a stable build currently seems impossible and switching from a dev to a stable build currently seems to need complete reinstalling, including data loss.