@Elder - I have the ASUS ROG Ally Z1 Extreme, and am very happy with it. In fact, I use it more than my PS5.
However, if battery life is something you're concerned about, then the ROG Ally X would be the way to go.
To add to what Tea said, the Ally is a Windows-based device... So, you'll be dealing with Win 11, which may or may not be a good thing depending on how you feel about Windows.
There's also quite a lot of initial setup. Apps need installing and updating, Windows needs updating, etc...
In terms of compatibility with other platforms, as well as hardware capability, then the Ally would be good for you: Gamepass, EA Play, Ubisoft Connect, GOG, Steam... Being a Windows-based device, it can run them all! Hope this helps. Sorry for the essay...
Look Steamdeck is highly optimised and great if you have an expanded steam library that would be your choice but for game pass and other platforms you want to use, ASUS is the winner, just may not be as optimsed a gaming handheld experience
Help a veteran here because I don’t which way to lean. I’m very interested in getting a handheld PC. There is an endless selection and after doing some research it seems that the Steam Deck is an obvious choice, but seeing that it doesn’t support Game Pass PC, which handheld will deliver better and or equal to Steam’s device and running Game Pass PC without all the tedious setups and modding. From the box, I want to remove the device and start playing.