No style & no redirection for admin dashboard

Hi everyone,

So to explain my problem in as much detail as possible: I updated wordress to the latest version (#5.8.3) with the plugins and my theme. However, I had a problem: When I want to press any item in my admin dashboard, I am redirected to a blank page of ‘No template maching found’ (Error 404 I suppose). This is the case for every node after example.com/wp-admin/*. Namely, the wp-admin index.php page displays correctly and the basic site is all good, it’s just all the wp-admin pages that have problems.
Here is what I tried:
1. Enable debugging, without success since no entry indicates an error that could cause this problem.
2. Disable all plugins, without success.
3. Disable my only theme, without success and it breaks example.com.

I don’t know much about wordpress and the problem in this case is that I can’t administer anything since I have no access to it.

Thank you for your support.