I keep a copy of the apk for all my apps, using something like APK Extractor - it extracts to a specific folder, and I sync that folder to my desktop using Syncthing. I haven't installed GSam from the store in years.
main issue is that i purchased the pro, and there's only the free over there... wait! I can take the apk from the old phone before I wipe it! OMG why i didn't thought of that, i'm dumb. (no sarcasm, I actually forgot to take the apk from the old phone and i was about to wipe it! Thank you for mentioning that!)
edit: fuck.... on android 15 the app crashes when going in background... so it's the dev that intentionally delisted for everyone as low sales = patch not worth the time 😢
No it shouldn't validate the license, at the time I purchased it using a Google workspace legacy account and when they raised the prices I deleted the account and it didn't complain
Put the apk on an old android 8 phone and doesn't crash. One day I'll try to inspect logcat to see if it's something that can be fixed