so i downloaded Lubuntu 2 months ago using the help of a youtube video, some issues happened like the grubhub got installed on the flash drive(solved) and certain games wouldn't run(have to run a command before opening them)

But i couldn't solve some other problems like:

some sever screen tearing that's highly noticeable

and i tried installing a new theme but it wasn't apllied correctly
only the colors of the themes would get applied if that makes any sence? the interface didn't change at all basically nothing changed, i tried the recommended theme format and that didn't workd i tried the Kvantum ones and they still didn't work,
what's weird though is that when i looked at a tutorial it said to go to prefrences then go to customize look and feel, i couldn't find "customize look and feel" though the closest thing to it was "appearance".

i originally downloaded Lubuntu because i have an extremely old pc that was struggling with windows10 but somehow it got slower when i installed Lubuntu.

so i don't get it, is Lubuntu not compatibale with my cpu(core 2 duo) or something?