Oh, so that's why it didn't go up to 120 before!
I've been investigating and it seems like it's a driver problem (NVIDIA in my case) and not a SFML one. Turning off "Threaded Optimization" in NVIDIA Control Panel solved it. I guess that's a partial win 😅
Going off on a slight tangent, I've noticed the FPS determine the physics movements and I came across this article that might be helpful to make them consistent
I hope all of this helps!