Actually I tried out KDE Plasma on my grandmother’s budget laptop from about the same time. It was a little too slow with default settings, but once I killed the animations (can be done in Settings app) it ran pretty well. It ran a whole hell of a lot better than the Windows it came with.

I also tested KDE vs XFCE in my old gaming computer, and I actually managed to get slightly less RAM usage in KDE than XFCE, so long as no plugins were used.

Both systems were tested with Debian 12. On the gaming PC, I actually used the XFCE iso, so it was installed first.

So depending on how your distro ships the default KDE Plasma settings or how you set it up, it actually can be a lightweight option compared with XFCE.