Hi @pgr,
I don’t know how that works with Debian means, I dislike using any means of installing software unless its the way it comes with Debian sumply to have the advantage of easy to update security fixes. I have installed a Debian 11 system and there the upgrade worked but still had to read up on an issue where the Admin page would remain empty. The link below helped me fixing that issue.
https://community.suitecrm.com/t/unable-to-view-admin-page-after-installing-7-12/83188/3
Thank you
Jan P.