Yes - I noted that - plasma is not more demanding than xfce - and yes the CPU and available RAM leaves litte to no room for optimization.
There is only one way to tweak performance - go pure wm - openbox becomes the obvious choice.
This can be achieved using a community edition, see the → Spins category
→ SbK LXQt 24.2.1
→ https://maboxlinux.org (Mabox Linux - Browse Files at SourceForge.net)