I was able to solve it.
Checked what was the password in the wp-config.php;
/** MySQL database password */
define( 'DB_PASSWORD', '<removed>' );
Copied that value and reset the password in WordPress extension -> WordPress instance -> Database tab -> Database user name and click on [change]...
I've migrated from Plesk on one server to Plesk to another (ubuntu 18 to ubuntu 24). I know there is a database upgrade that happened between those releases. All works, wordpress sites are accessible until I try to do any maintenance (upgrade wordpress or even create a backup).
If I try to do...