if you use/tick sprint and set mine cart, max speed game rule to 1000 and a player gets in it and you wait for a while for it to get super fast and another player goes to the nether and comes back from the nether and presses a button to make the Minecraft cart to get released really high the mine cart and the player inside will go to the other place according to the server, but on the client side, the player is still going around in the track really fast. (I will add video later. me and my friend were messing around on 1.21.2 pre release 5 server)