Projectile which has effects when hit entity.

Make a ranged item for your projectile(make sure you set it so it doesn't need ammo), go to triggers and there is one that says "when projectile hits living entity". Put your freezing effect and all into that and you can make your ranged item have 1 durability or you could shoot projectiles using the "shoot ranged item as projectile" block. I'm using 1.16.5 so the procedure block might be different though you should be able to find it if you search "shoot" in the search bar.