Only works/happens in Datapacks!

Create a datapack with a function with this commands:
(Download kaths-Teleporter and run /function k_tel:test)

ride @s dismount
tp @e[type=minecraft:horse,limit=1,sort=nearest] ^ ^ ^10
tp @s ^ ^ ^10

Ride a horse and run the function.
The horse will get teleported but not the player.

I'm working on a teleportation datapack and on versions 1.21 to 1.21.3 the player will get teleported but while I was testing the datapack on 1.21.4 I noticed the player will not get teleported anymore if they are riding a horse.