Python 3.8 works if you set the soft-link as described here.
In terms of restoring the following might work, though not sure because of the different python versions.
Install 7.1.4 on your new SD card. Copy the “ccnet”, “conf”, “seahub-data” and “seafile-data” folders as well as the “seahub.db” from your backup to the new location. Run all update scripts from 7.0.4 to 7.1.4. Hope that Seafile and Seahub start…