any special entity?

Is there any type of entity that when you tie it to a trigger or something, it doesn’t allow people to spawn props? or would I have to make a gamemode for things like this?

You would need a lua script.

There is an entity to remove all physical props instantly, that would have the same effect. But if you want previously spawned props to be there then it’s not going to work.

So if i were to use a lua script, could I embed this into the map or would i have to make this separate and how would i go about writing this?

You could put an entity in there that has no real use in Hammer, but when the map is run with the script, the script recognizes that special useless entity and makes it where that entity has a purpose in the game. Example
info_player_team1 - custom spawnpoint for team 1, no coding involved. Will show as obsolete in Hammer.
info_player_team2 - custom spawnpoint for team 2, no coding involved. Will show as obsolete in Hammer.
When the script is run on the map, if the script has something in there to recognize info_player_team1 or team2, if you chose your team, for example, which would be team1, you would spawn at the info_player_team1 place. If your friend joined and picked team 2, the script would send him on his merry way to info_player_team2.
I hope that helped.