I’ve had best smoothness in sim (old habits die hard) with using VSYNC set to fraction of monitor refresh rate. So think 120Hz/40FPS, 60Hz/30FPS, 60Hz/20FPS. That was generally true in FS2020 but is also true in FS2024 it would seem. Others may argue otherwise, but visual smoothness is what I’m happiest looking at regardless of anything else. I find that before adding in lossless scaling, if you don’t have that smoothness set up already, then you can just add to the problem despite seeing more ‘FPS’ count with lossless scaling. So try making the default sim settings run smoother first.
I find that my system is very happy to produce 20FPS continuous at 4K native, you can throw lots of complex scenery at it and it generally stays on 20FPS, so thats what I call a smooth/steady 20FPS. If you have it targeted at 30FPS, depending on what you are doing you will see dips below 30FPS, so it isn’t a smooth/steady state.
Now 20FPS although steady isn’t desirable as optically you do notice 20FPS, but that’s where lossless scaling come into it’s own and makes that steady 20FPS into 60FPS which is mostly all smooth and minus stutters for the most part.
That’s how I see it, but everyone may have their own opinion based on what they see visually.