
Run silky smooth for a vast majority of Shadow Generations. Vastly superior experience compared to the Switch version.
Shadow Generations does not support 16:10.
At a mix of high and low graphics settings, Shadow Generations runs at a very consistent 60fps.
The framerate does tend to drop in mid-gameplay cutscenes, but that's not too big of a deal since you're not actually doing anything in them.

Turn everything to low at 720p/75% scaling at 50 fps
720p at 75% scaling with 50 fps and a TDP limit of 10
If you are on Steam Deck, just cap it to 50 fps. Sonic Gens, once you get to the raw numbers, isn't as smooth with a wild frametime graph, but you aren't very likely to notice it while playing, and Shadow Gens runs like a dream.

Will lock to 60fps at 720p if Shadows and Volumetric Lighting are set to Low.

Only settings changed were in Shadow Generations, all settings low. Sonic Generations all high and both run at 60.
Runs as if it were made for the Steam Deck

Note that I haven't completed it yet, but from what I've played it works great, at least at 1080p. There's a bit of lag in certain areas.
Display Settings: Brightness: 50 Graphic: Custom Shadow: Low Framerate 60 Anti-Aliasing: FXAA Ambient Occlusion: None Local Reflection: None Bloom: Low Volumetric Lighting: Low Resolution: 1920 x 1080 Resolution Scale: 75% Vsync: Enable
This may be a bit different for you, since I'm using it at 1080p. I'd say use these settings, just to be safe though.

Opening Cutscene after Green Hill Act 1 stuttered a bit.
Forgot that these can't be updated or removed...again...so this is to let you know that I played both acts of Chemical Plant Zone, and battery only went down 7-8% during thattike, so there's no major battery drain issue like I thought. Odd that it doesn't have an official rating yet, but I imagine they're waiting till Friday.

Change graphics setting to low for 60fps
Default graphics runs between 45-60 depending on the stage. For a consistent 60fps change the graphics to low and set the fps counter to 60

Sonic Generations runs as expected with a sustained max frame rate and barely any frame drops. Some minor bugs can occur, but nothing that absolutely breaks the game.
With the default graphics settings, Shadow Generations runs well, with some dips in frame rate in busy scenes, but otherwise runs very well in the White Space. Actions could be taken to improve performance, but default is not a bad option. Barely any bugs were encountered and the experience overall was smooth enough.
Both Sonic & Shadow campaigns run great at 60FPS on High settings and default launch setup.
Worked perfectly straight out of the box with Deck refresh rate set to 60Hz. Some framerate drops here and there to mid 40s lowest.

There was a bit of stuttering during the birthday party cutscene for the Sonic half of this game.
Only played for about 14 minutes, but it seems to work fine. I think the default graphics are a bit of a battery drainer, at least for the LCD Deck. Though, I don't remember what percentage my battery was at, so if I'm able to update once I start it again and see what the battery power remaining is, I'll do so.