Great, the touchpads are amazing for mouse-related stuff while handheld. I can comfortably use mouse heavy menus with them. Obviously, a lot closer to a laptop touchpad than an actual mouse, but still a lot better than a joystick as mouse.
A Steam Deck is a PC. If you dock it, you can hook up a mouse+KB and a monitor, and use “desktop mode” (KDE plasma) to use it exactly like any other Linux desktop. Docked “gaming mode” makes it feel more like a home console for PC games (and emulators). It is even possible (though not recommended) to install Windows.