mariadb issues

Since I upgraded from 15.1 to 15.2, I can no longer access my mariadb databases from my local Drupal instances. phpMyAdmin lets me connect, and the databases are all there, as are the user accounts. But phpMyAdmin says The mbstring PHP extension was not found and you seem to be using a multibyte charset. Without the mbstring extension phpMyAdmin is unable to split strings correctly and it may result in unexpected results.

However, mbstring is installed for php7. phpinfo says that Multibyte String Functions are installed.
There are no entries in /var/log/mysql/*. PHP is PHP Version 7.4.6
I could use some suggestions as where to look next.
Thanks for any help.

Don’t know if I’m right but I interpret the error you’ve shown as a PHPMyAdmin possible problem, and not necessarily a problem related to your MariaDB.

You may have a different problem with your MariaDB.
I haven’t looked specifically at what versions of MariaDB was standard in 15.1 and what is the standard version in 15.2, but it’s fairly common for server apps to upgrade their versions at the same time as system upgrades.

Recommend you verify your Drupal error with whatever errors can be collected… I personally haven’t run Drupal for awhile so can’t account for how it logs errors today, but you should check that. And, look for your MariaDB errors, I would expect them to be in your journal (ie run journalctl to query).

Are you using anything else besides PHPMyAdmin to manage your system?
Have you used any other apps like mysql workbench?

This is a word of caution for others who are upgrading systems running server apps…

If this is your first server upgrade, ASK QUESTIONS FIRST.
You need to research the consequences of the server apps running on your system, you will often need to upgrade those separately, they rarely are upgraded automatically by a system upgrade.