Keyboard input lagging a lot since upgrade of Windows 11 to 24H2; how to fix it?

Microsoft decided to upgrade my Windows 11 Pro to 24H2 on my Lenovo P16 laptop yesterday.

As usual it took virtually forever (I’m talking about two hours from “40%” done until ready for reboot) watching the “progress” (if you want to use that name), even though the machine has a Intel i9 CPU, more than 64GB of RAM and a Samsung 990 Pro SSD.
Only my VDSL line is not that fast.

But anyway after the first boot and being logged in, I noticed that entering a text in LibreOffice Writer was delayed significantly (like one second) occasionally.
At that time I thought “Well, Windows is doing some background tasks that delay interrupts, or whatever”.

But one day later I still see lagging keyboard input, for example filling out text input fields in the Firefox browser.
I’m not a fast typer, but that makes the laptop almost unusable.
Also (in case someone would ask): The laptop was running on AC power all the time.

So I wonder: Is this a known problem, what causes it; and is there a fix for it (other than reverting to the previous version)?