Experience with PHP-FPM and mariadb heigh load

[ufgum]

Steps to reproduce

I have various IMAP accounts with a total of around 200,000 emails. Since the last update, the mail app is hardly usable anymore because when you call up the mariadb server works long time until the server can hardly be reached anymore. The server isn't super fast because it's an Intel NUC, but it's always been sufficient so far.
If I run an "occ mail:account:sync" on my accounts, I can use the Mail APP again for about a day. The cron jobs also run reliably, nothing has changed so far.

My problem now is that I did a Debian update from 10 to 12, so I also switched from PHP to PHP-FPM with opcache, and immediately afterwards did a Nextcloud with Mail APP update. So of course all traceability is lost.

However, I strongly suspect PHP-FPM and wanted to ask if anyone has any experience comparing the mail APP with PHP or PHP-FPM in relation to mariadb utilization?

Expected behavior

less db activity

Actual behavior

heavy db activity

Mail app version

3.6.0

Mailserver or service

dovecot on same machine

Operating system

debia 12

PHP engine version

PHP 8.1

Web server

Apache (supported)

Database

MariaDB

Additional info

No response