the stability of the 120 fps of the multiplayer H3 is better in SX or in SS?

I have seen in videos that in the H3 multi the frames drop to 110-90 fps in Series S in Series X they stay at 120 fps or do they drop?

I have a series x and haven’t felt any drops in fps in halo 3 campaign and multiplayer. Halo CE and Halo 2 in classic mode run fine. I’ve noticed drops in H2A, H4 and Reach.
I’ve only ever noticed drops on Reach in certain forge made maps but If you enable VRR it’s hard to notice.

Edit: Can’t say for sure but now I remember that the map waterfall that was added to H3 has slight performance issues on SX.