Can’t install any plugins

Sounds like you might be on a multi-site, in which you have to be super-admin, and go into a slightly different area in order to get the Add plugin button.

Here is a good place to see screenshots of where to add plugins, if you have a multisite:
https://www.wpbeginner.com/beginners-guide/why-do-you-not-see-all-plugins-on-wordpress-multisite-installs/

If you don’t want to spend the necessary time figuring it out, I suggest that you hire a web developer to troubleshoot it for you.

It would seem that they have deliberately limited your admin access so you can’t ‘break thing’ because ‘they manage it’ ( even though you say they don’t ) this is not uncommon in managed services.

Do you have access to the file system on the server e.g. via FTP, or SSH or a Control Panel with a file manager?

Or as above – you have been setup as a multi-site.

Hello there!

I’d say see if you can replicate some of the issues with a new administrator user. 1and1’s Managed Hosting might have some must-use/drop-in plugins that might be causing some of this behavior.

As for the auto-updates, there might be something within the wp-config that’s keeping the site from being updated automatically.

After looking at 1and1’s Managed Hosting page, it looks like the auto-updates has to be enabled somewhere.

This is about switching from Managed WordPress to Standard but it might help provide a clue as to what’s going on.

https://www.ionos.com/help/websites-stores/set-up-wordpress-at-11-ionos/changing-from-managed-wordpress-to-standard-mode/

It’s also possible there may be some type of plugin(s)/theme conflict that’s occurring. You can open a browser console and replicate the issue to see if there is a 500 error that’s being generated. Here are some resources for opening a browser console.

https://developer.mozilla.org/en-US/docs/Tools/Browser_Console
https://developers.google.com/web/tools/chrome-devtools/open

If you do not uses these browsers go ahead Google search how to open a browser console for your primary browser.

I hope this helps!

Thanks a lot for your advice!!!
I just solved the problem by editing wp-config.php.

define(‘DISALLOW_FILE_EDIT’, false);
define(‘DISALLOW_FILE_MODS’, false);

Found another poor soul with the same problem und tried his solution.
I hope, I didn’t do any damage, but so far it seems to be working.

No you won’t do any damage.

But personally I would turn back on
define(‘DISALLOW_FILE_EDIT’, true);

as this controls the theme code editor and plugin code editor and it is generally a poor idea to have that enabled to allow code editing via the backend.

Thank you very very much, atxmatt and Fullworks.
I will change the file_edit command back to true again.