Plasma is pretty light these days and worth a look. I use xfce and plasma on my home/work machines, They're both mid 2010s I5 dell workstations, so old, but decent specs for a general purpose desktop. I feel no difference between them performance wise. Ram consumption is similar. I like both desktops, and I like having a foot in both gtk and qt, but sometimes I think I might want to switch my home machine to plasma. I never think I want to switch my work machine to xfce.
edit:
as an old sidenote... Around 2020 I installed lubuntu on my boss' c2d desktop, but the performance was pretty bad, especially for the features that were cut. It's supposed to be light, and it uses the lxqt environment. I then wiped it, and put kubuntu on it, and the performance was much better. It's an old data point, and wasn't thoroughly researched at the time, but it's worth noting.
Point is, old dogma sometimes doesn't hold up to time, and it's worth revisiting technology to see how it behaves on *your* specific hardware. Pick something you'd actually like to use, and see if it works well for you.
If I wanted to save every scrap of resources, I'd use a simple window manager instead of a full desktop. and trim everything out that isn't a feature I use. "Features" are "bloat". "Bloat" is "features". Semantics...