All non-binary documents vanished after upgrade to 5.4, only top level folders left

[kqcav]

But in a way you're up to something:
This group ›staff‹ is only defined in Cloudron, not in NC.

Maybe user_ldap also fetches group assignments from Cloudron no matter if defined in NC, wheras ›OpenID connect user backend‹ only fetches those available in the app / in NC.

I'll try that.

[kqcav]

No, that did not resolve the problem,
even if ›staff‹ is also a group in NC and the users are assigned to that group,
our files & folders (below top level) do not show up in the NC interface.

[kqcav]

Also:
independent of group assignments, NC doesn't even show a user's own files (but it probably should, shouldn't it?)