You have to edit your config.php (usually under /var/www/nextcloud/config/config.php), if you have this parameter already there, change it to false, if not you have to added it, because default value is true or previews enabled.
After you edit your config you have to do some DB cleanup as described above.
But how can i do the rescan WITHOUT occ access (no bash or ssh) on a shared hosted system ?
That is a very big problem with nextcloud (also running the index updates is not possible).
i disabled previewing in the config (months ago), but the folder contains still 12 GB (GIGAbyte !!!) files. why isn’t nextcloud automatically (and f.eg. successive) rescanning and cleaning those files ? can those files & folders within “/cloud/data/appdata_xyz12345678/preview” simply be deleted without loosing data ?
As you already noted: Not available for V19+ (and i am using V20 currently)
It is not cleaned automatically, you have to reclaim space
Yes. I recognized. But that would be an interesting question for the nc developers, WHY those settings are not checked by interval or cannot be triggered manually from the normal admin/user backend.
Run sudo -u www-data /usr/bin/php /var/www/nextcloud/occ files:scan-app-data to fix database
Simply not possible, because there is still no SSH or bash access.
That is simply bad developed, when space is filled up automatically - but for cleaning it you need manual action and special privileges. 12 GB is a lot of space for useless data … i think i have to replace nextcloud by another software.