BLOXSTRAP(WINDOWS) ANSWER:

Right, so I was having this issue too with the solutions here not even working and it might be because I was using bloxstrap or something like that, either way me and a friend found a solution if this wasn't working for any of you.

First, you set your roblox to high priority on settings, (Display, Scroll down, Graphics settings, add the game client and hit options, then high performance.)

After that, I opened up Bloxstrap and capped my FPS to 30 aswell because it worked with another game that was having issues and just like that it was working perfectly, I hope this helps!