Thanks, I am sure it will help when I will get to more complex apps (now working on vaultwarden…), and I am very anxious about nextcloud… I will report here.
UPDATE : I had at first 502 error after successful restore of vaultwarden, and a yunohost app upgrade vaultwarden --force did the job. Thanks also to [Résolu] Migration 64bits plantage vaultwarden
UPDATE 2 : I had a chown error during nextcloud restoration, tried this fix : One of my Nextcloud installs is missing after a system upgrade - #3 by colmoneill