WordPress login hangs: upgrade.php?_wp_http_referer=%2Fwp-admin%2F

WordPress login goes wrong?
White page and %Code in the URL?

Problem

After login,the page remains white and the browser URL contains this text:

"/upgrade.php?_wp_http_referer=%2Fwp-admin%2F"

Reason

WordPress tried an automatic update, it went wrong.

The files were updated, but the database was not. Now the database does not fit.

There should have been a dialog that WordPress needs a database update, which you can then start by pressing a button.

At this point, however, there is only a white page instead.

Our solution

We have successfully tested the following solution (WordPress 6.3 – August 2023):

1. Via FTP we go to the WordPress directory “wp-login”.
2. We open the file “update.php”.
3. There we change in the line
   “define( ‘WP_INSTALLING’, true );”
   the word “true” to “false”.
4. Now we do a refresh of the page and get the dialog we are looking for:
5. We click the update button.
6. We go into update and there on WordPress “reinstall” (this installs again everything cleanly and undoes among other things our change of the “upgrade.php”):
   

Ready!

Other solutions

Here are more suggested solutions:

https://www.developingsense.com/blog/problem-solved-upgrade-php_wp_http_referer/