1. Wait for some time to see if the problem will solve:
Normally the problem caused because of the database update, by waiting we will let WordPress do the update in the background. If the solution didn’t work, try solution 2.
2. Delete .htaccess file from your host:
The description below is from Daniel Morell’s website
htaccess (short for ‘hypertext access’) file is a distributed server configuration file. … htaccess file allows you to set server configurations for a specific directory. This could be the root directory for your website or an /images or /downloads directory. It is used on the Apache webserver.
By deleting the .htaccess file, we will reset the server configuration, so if by deleting the file, the problem still exists, try the third solution.
3. Downgrade your PHP version:
This solution worked for me. I Downgraded the PHP version of the website to version 7.2.34 (outdated)! I know it may sound crazy but most of the time by downgrading the PHP version we will go back in time. Then I went to my WordPress admin dashboard, It loaded correctly this time. I updated the database without a problem and then updated the PHP version to version 7.3.27 (most recent PHP version) and then went back to WP admin dashboard and Baaam! Everything back to normal.