403 Forbidden Error in Panel V4 Update

Hello,
I am currently updating my app from 3.9 to 4.0 and getting a 403 (Forbidden) error when logging in to the panel with the admin user. The app itself works just fine. Does someone know what the problem could be? Thank you!

Did you clear the media folder (and the cache ) while updating?

Yes, I did.

I assume you have updated to the latest 4.x version, i.e. 4.0.3?

Then the next step would be to make sure you are not using any incompatible plugins.

Please also check what you get in the browser console (with debugging enabled) and if you get more details in the php/server error logs.

Yes, I updated to 4.0.3.
I removed all Plugins but it didn’t worked either.
Debugging is enabled and the console shows

GET http://localhost/admin/panel/pages/termine 403 (Forbidden)

There are no errors in the server log.

This is my user object:

return [
    'email' => 'myEmailAddress',
    'language' => 'de',
    'name' => 'carolin',
    'role' => 'admin',
];

Do you have any other idea?
Thank you!!

Does this happen in your local development environment or on the remote server?

What is your setup (PHP version, server etc.)?

Did you make any changes other than updating Kirby, like change the PHP version, for example?

Also make sure to clear the browser cache.

It happens in my local environment as well as on a remote server.
Locally, I have PHP 8.1.2 and the newest apache version installed. On the server, it’s also PHP 8.1
I changed the PHP Version from 8.0 to 8.1 for the update.
I also cleared the cache and built a new Docker container.

O, could you please double-check that your new PHP version fullfills all requirements: Get up and running | Kirby CMS

I checked the requirements again and I have all the php extensions and the supported PHP Version installed.

The login itself works but I after the login I can’t access the Panel with any admin user.