Looking to get the latest Firefox Preview version for DarkReader addon support I stumbled upon "fennec-production":
https://firefox-ci-tc.services.mozilla.com/tasks/index/project.mobile.fenix.v2.fennec-production/latest
After installing this version I realized I'm a dumbass because unwantedly it replaced my current Firefox for Android install from the Play Store instead of installing an update to my existing Firefox Preview.

However unexpectedly once I opened the fennec-production build I was greeted by a migration screen with checkmarks (history, account, addons...) and after around 20 seconds it was done. And it worked just fine. All my roughly 120 open tabs were migrated, my Firefox account, addons (although Dark Reader is still in disabled state), history...