I've not seen this actual problem myself but a few people have reported it on a fresh installation. Unfortunately, we don't ever seem to hear what the resolution was.
I have a couple of thoughts on the matter.
Firstly, the later versions of Windows 10 seem a lot more memory hungry than previous versions. For example, I have a couple of old PC's that can't take more than 4GB RAM and they worked acceptably well on 1909 but are virtually unusable on 2004 and even worse on 20h2.
There also seems to have been changes made to some of the drivers and a number of older devices that I have in those PCs won't work properly any more (if at all).
Subjectively, there seems to be a lot more disk activity on those PCs with recent versions than before as well. Maybe paging to disk?
Lastly, the systems seem to take much longer to settle down and to finish installing all the new features (bloatware) that MS seem to install nowadays.
Maybe it is a combination of all these things?
Discussion of getting WMC to work on Windows 10 (unsupported)