Highjumping tldr; Hold Print Screen and jump when it lags completely.
-Hold crouch(If you want to do the high crouch jump) -Hold printscreen (It will do a small lag then run the game for like 1s and then it will basically freeze the game) -When it freezes press jump. -release print screen whenever you did your trick.
The lag will exit when you press any key so you need to hold crouch before doing it. You can also hold W to move forward and then PrtScrn + jump to get a higher normal jump while walking.
I hope this helps