If you run on an Realm "/execute as @s positioned ~~~ [...]" or "/execute as @s positioned as @s [...]" it says an error at ~~~ or as. If you do instead "/execute positioned ~~~ [...]" it will not return an error. If you do "/execute as @s positioned 0 32 563 [...]" (fixed coordinates) it will not return an error too.

On my world it works all fine, but only on the realm not.