Upgrades are easy, backups are really good, if upgrades mess up, you can restore from backup even if NC is hosed. As for local storage, I never did it, but here’s the docs for it! https://docs.nextcloud.com/server/latest/admin_manual/configuration_files/external_storage/local.html

Crippling is a bit extreme - have you used Proton recently?

https://protondb.com/

Check the list, bud. It’s far from just obscura.