Apparently kernel 6.1.41-1 is still affected by this issue below… 
I don’t think it would be an actual CPU load of 100% on that particular core, though, because if that were the case, then the temperature readout for that particular core would be a lot higher than can be seen in the second screenshot here-above.
On my system, that particular core always runs just a tad hotter than the other cores anyway, but its current temperature readout of 36°C is not consistent with a core that’s genuinely stuck at 100% — in that case, the temperature readout would probably be somewhere in the 40-50°C range.
So whatever’s causing this apparent 100% load is most likely a bug in the kernel code reporting the core temperatures, and according to the 2023-07-25 Testing update thread, the issue was apparently fixed in 6.4.6. I guess no one thought of backporting it to 6.1 as well. 
Oh, and on account of mariadb being the cause — which I doubt, although it may be the trigger — replacing it by postgresql is not an option here because I’m running Plasma, and akonadi requires mariadb. I don’t know whether it would be possible to replace mariadb by mysql proper — I’ll have to investigate that — but mysql is an AUR package, and I would rather not replace an essential component for my desktop environment by an AUR package.
