I haven't tried Plasma 6 on my 2013 laptop with a slow spinning rust disk, but Plasma 5 is fine. Way better than Windows 10 which i rageformatted when it took hours to apply some stupid update and i almost lost a business video call (my laptop is the only PC i have with a camera).

I installed openSUSE Tumbleweed which sadly seems far from I/O efficient, not sure why (there is almost a hundred of background processes doing who knows what). Perhaps a lightweight distro would be better since i mainly use it to make calls or try out some graphics code (it is the only Nvidia device i have), but while it takes a couple of minutes to boot up, once it does it works fine so i don't mind much as i'm only rarely using that machine.

Disabling file indexing probably goes a long way.