solved!
Managed to find a solution that fixed - at least for me - the glitching (now the game runs normally with no graphic issue also on "ultra" quality) and also the crashing problem that, I hadn't noticed before, but whenever I tried to play a saved or new game, once I was about to load the household would crash me out of the game.
All I did was resetting the game to factory setting, following the steps on a blog that was linked on an older thread
here you go, hope this helps someone!
link to old FAQ thread: https://answers.ea.com/t5/Technical-Issues-PC/FAQ-Sims-4-Crashes/td-p/3586547
link to blog page: https://sims4.crinrict.com/eng/2014/09/resetting-the-game-to-factory-settings-without-reinstalling/
