First, although it seems too simple to be true, do try and make sure that it isnt your internet connection that is causing the lag. You may be experiencing a spike of disconnected or reduced internet speeds. Another reason you might be experiencing Halo Reach PC lag is that you are playing with uncapped framerate.

How do I increase my FPS in Halo: Reach?

3:177:30Halo MCC: How To Increase FPS! - YouTubeYouTubeStart of suggested clipEnd of suggested clipJust go to options. And career then go to settings. Then go to video scroll. Down and then look atMoreJust go to options. And career then go to settings. Then go to video scroll. Down and then look at graphics quality and change it from enhanced or original.

Is Halo 4K 120 fps infinite?

On the Xbox Series X, the Halo Infinite beta runs at 4K resolution, and though it targets 120 FPS, the performance generally hovers in the 100-110 FPS range, while sometimes dropping into the 90s as well.