Xbox Series S Settings - 1080p 120hz, VRR On, HDR Off. MW2 Settings - 120hz, 120fov, FidelityFX CAS Strength 100.

First thing, compare the network speed and statistics on your console as well as on speedtest using a laptop or mobile device. On your Xbox: Settings > General > Network Settings > Test Network Speed and Statistics. If it's the same and indeed high ping on both, the issue can be with your network connection.