The "/spreadplayers" command doesn't spread entities in the specified dimension.
When using the spreadplayers command in combination with execute in <dimension>, for example:
the players will be positioned as if they were spread in the given dimension but they will remain in the dimension they were in before.
- Enter the overworld if not in it already.
- Use the "/spreadplayers" command in an attempt to spread players in the nether dimension by using the command provided below.
- Take note of how the players are spread to the specified coordinates but remain in the overworld instead of being teleported to the specified dimension.
Entities are teleported to the said coordinates but remain in the dimension that they were currently in when the command was executed.
Entities would be teleported to the said coordinates in the specified dimension.