Agree @Mayhem6633, I also prefer to play capped for that reason (I use lower quality such that my cap can be somewhere between 40-45 rather than 31 fps; need to play more with it to find a sweet spot for me; 31 fps is consistent but it feels a little bit too choppy for me).
I cannot prove this now, but back then when I tested with motion reprojection I had set the cap to 31 fps via Adrenalin driver. And in that case the in-focus MSFS was stuttering like hell (it showed ~22.5 fps in the OpenXR overlay reprojected to ~80 fps) whereas the no-focus MSFS could hold its ~30 fps reprojected to 90 fps which felt very smooth. So my impression was similar to what @mark007777 observed: It felt like some VSYNC was active when the game was in-focus. Similar thing I do observe with DCS: With in-focus its exactly 60 fps fixed in my test scene, not more, not less. With no-focus it’s 74 (just measured it; my 60 → 82 from above were little bit exaggerated…). If I set higher quality in DCS, the in-focus DCS drops from exactly 60 to exactly 45. Could be coincidence and I need to test more with other settings, but right now it looks like some active VSYNC in the in-focus case.