Last post on the thread indicates its a mariadb issue
(being leveraged by akonadi because of Kalendar)
I found the process that was using a lot of IO-Wait to the CPU. It was MariaDB (11.0.2).
I use Kalendar as my Calendar program since i use KDE Plasma and this program uses Akonadi which uses MariaDB to store data on it.
Can you confirm this ?
PS. I leave this here for those who may wish to try a different DB with Akonadi:
https://wiki.archlinux.org/title/KDE#Akonadi