Reverting (disabling) MySQL 4-byte support - broken login page

I tried to enable MySQL 4-byte support using the docs and now my login page looks like this: Imgur: The magic of the Internet

I believe it’s because of that. When I open console in my browser, it shows this: broken nextcloud login screen - Album on Imgur

I want to try to revert it.

I think I don’t have to revert step one, because innodb_file_per_table was set to 1 already.

In step five, I just have to set boolean mysql.utf8mb4 to false. That’s not a problem.

But what should I do to revert step 4: ALTER DATABASE nextcloud CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci;?

Or does anyone know another solution to this problem?

Details: I run nextcloud on Raspberry Pi 4 on my local network at localhost/nextcloud. I am using apache as the web server. Nextcloud works (sync, browsing files,…) but I can’t login, so I can access only my nonadmin account to which I am logged in (thanks cookies) and I can access it also using terminal.