Performance is the same regardless of whether it’s docked or handheld, assuming the same render resolution. Rendering at a higher resolution will obviously negatively impact performance, so you’ll likely need to rely on heavy upscaling in a lot of cases.

If my game doesn’t run at 60fps docked in 1080p, I’ll usually just try something like 900/720p with FSR and it works very well

Textures don’t have much of an impact except vram so you can keep them nice and high, but the rest generally needs to drop on demanding games, shadows, reflections, lighting etc.

Variable

All titles run the exact same Docked as in Handheld, the Steam Deck makes no difference between if it’s outputting to TV or not.

Diablo 4 runs well

I run mine docked on a 4k TV and it looks fine just with fsr. This will obviously vary depending on TV though and how close you sit