On PC, the minimum render resolution Halo Infinite will let you select in-game is 768p; neither the resolution scale slider nor the dynamic resolution system will allow the resolution to drop further than this. On desktop, this is typically fine, but on handhelds like the Steam Deck it presents a problem, as their screen resolutions already being around that point makes dynamic resolution options effectively unusable.
It would be great if lower options were available; lower render resolutions than 768p still seem to work perfectly fine, as forcing the static render resolution below that point in the config files hasn’t caused any issues as far as I can tell. That’s obviously not an ideal solution though, especially since the dynamic scaler is still off the table.