for some reason obs randomly started lagging I have a mac can someone tell me their setting to make it not lag.

use a less cpu-intensive preset. use a lower bitrate. get a pc twice as good for a third of the price.

What type of Mac? Generally they are quite capable (albeit a bit over priced), so it makes me wonder if you are using hardware acceleration when you should be using your CPU. Make sure you have your encoder set to Software on the Advanced tab in settings.