A very unscientific and anecdotal comparison of KDE Plasma on Kubuntu 22.04 and my install on FreeBSD at the very moment I am looking at both: the memory usage seems similar overall, but individual processes seem oddly different. Example, kded5 on kubuntu (kde version 5.24.4) is using ~57 MB of memory, on FreeBSD (kde version 5.24.5) uses ~112MB. For kwin_x11, ~61MB on kubuntu, 140MB on FreeBSD. I restarted Xorg on FreeBSD and that's what they booted up to.
This is interesting why it uses a bit more memory on FreeBSD, but there is probably some reasoning behind it.
Take a look at the end of article where I added also freecolor(1) and htop(1) memory usage - it seems to be a lot lower then RSS field from top(1) command.
This is interesting why it uses a bit more memory on FreeBSD, but there is probably some reasoning behind it.