macOS temporarily freezes
TL;DR
I found out that my problem was caused by the no longer maintained MagicPrefs software. Uninstalled it, problem gone!
How I found the culprit
Today the problem occurred again, and I think I managed to find the culprit! Once the problem occurred, I opened Activity Monitor to see if I could spot some process doing weird. The first thing I noticed, was that the CPU load was low overall. No processes were taking up more than 20% CPU.
Then I right clicked on the column headers to add some more columns, hoping I would find a clue. I added the column showing if a process was unexpectedly stopped. (My MacOS is set to Dutch, the column is called Plots. beëind. in Dutch, I don't know the exact column name in English.) I immediately noticed that the hidd process had a &quot;Yes&quot; in that column.
So I went Googling and found this explanation of what the hidd process is. It's the Human Interface Device Daemon. The article states:

If high resource usage persists, the likely culprit is third party software. If you’ve recently installed drivers for a third party input device, or software that lets you do things like customize your key bindings, this could hypothetically be the issue. Try uninstalling this software, then see if that solves the issue.

That made me think about software I have installed that has to do with Human Interface Devices. There wasn't anything installed recently, but I was using MagicPrefs for some years. I went to their website to see if there were any updates and saw this notice:

MagicPrefs is more than 5 years old now and is no longer mantained, the functionality it provided was made possible by Api's that are now deprecated and reverse engineered private Apple frameworks. Apple is not likely to replace the deprecated Api's nor provide access to the underlying multitouch technology so that's the end of the line for MagicPrefs and similar software.
TLDR if it doesn't work anymore thats it, if it still works then its just a matter of time until it won't.

When I uninstalled MagicPrefs, the freezing problem immediately disappeared! I think that proofs that MagicPrefs was the culprit. A pity I can't middle click any more, but I'm relieved that this weird problem is gone now!