The oldest intact building in my city is from 1320 - so 700 years old. Baguely Hall, which is an old landowners hall.
The city itself - Manchester - dates back to the roman era and we have the remnants of an old castrum/fort in the city centre dating back to 79 AD - so 1945 years old. Surprisingly there were more complete ruins at the site but much of it was levelled during the industrial revolution.
Just on the KDE front, I’m assuming you’ve optimised your KDE set up for your PC?
If not, first open your Settings app and in the search box type “Effects” - disable all the fancy desktop effects.
Next, if you’re on X11, go into the “Display and Monitor” section and disable compositing (you can also temporairly disable this with Alt+Shift+F12 to see what impact it has). This option is not available in Wayland; but you may be better using X11 if you don’t have a dedicated GPU? I’m not sure I’d be messing with Wayland on an old laptop; I’ve had serious issues on a high end PC - definitely improved with 6.1, but I’m using X11 still.
But KDE 6 isn’t as svelt as KDE 5 was, so even optimised it may just not be up to the job.
XFCE is a good shout, and should run nicely on a 2013 laptop.