dev gets OTA updates just fine, but since /e/OS only supports one underlying Android version at a time on a device, and since update support for any given Android version will end somewhen, /e/OS has to be upgraded to a new Android version from time to time to continue to get updates.
/e/OS developers put in quite some effort to release OTA upgrades to new Android versions without data loss (hopefully) on a few select devices (FP3 among them), but only on stable, not on dev … see https://community.e.foundation/tag/development-updates. For all other builds or devices this upgrading process is manual, with data loss by default.
Well done 
… and with the change to stable you are set to receive an OTA upgrade without data loss (hopefully) to Android 13 (T), if and when it would come to pass …