Upgrades of the underlying Android version are done by doing manual new installs, unless the possibility to do an upgrade via the OS updater is specified in section “OS OTA upgrades” in the development updates … https://community.e.foundation/tag/development-updates
OTA upgrades will have to be prepared by developers per device per upgrade step.
By default user data will be wiped with manual installs, unless users can report that they somehow upgraded a device successfully without wiping data. Example: FP2: upgrade from Q to R advisable? - #11 by ingolf