[SOLVED] VSync stuck at 75 fps instead of 144 fps

I have found a solution for this problem!

Put ~/.config/kwinrc in Konsole
Add MaxFPS=144 to the [Compositing] section.
Restart your computer

Sources:

https://www.reddit.com/r/kde/comments/cwedej/comment/eyaqmnk/?context=3

Thank you filo!