I got this by getting on a strider with a fungus on a stick, walking forwards and placing a boat just in front of the strider.

This bug causes the player to get off the strider and be able to move around normally while the strider is stuck in mid air, if the player presses shift they will teleport back to the strider and the strider will get unfrozen.

I have very inconsistently been able to break or place blocks in this state, sometimes they just break for one frame and come back, sometimes i can only break a couple, and sometimes i can break a seemingly unlimited amount.

I have not yet tested this in multiplayer.

Edit,: You can also not interact with entities or go through portals, and if you try to use a command that does something at the location of the player, it will happen at the location of the strider