Jaarknstein: So maybe it's there for you, fingers crossed, but mine is access by the following:
• Click Multiplayer on the main menu
• Look to the right hand of the screen for Direct connect. There should be a checkbox, check it.
• Enter or paste Direct ID
If theres no checkbox (before_resize.png), I had to do the following, as changing the aspect and resolution did no fix it...:
• Open settings > Video > Displaymode = Windowed
• Goto multiplayer screen, if checkbox is not there, then widen window by dragging to resize.
• Checkbox should eventually appear, continue as mentioned above.
• Once in server, goto options and switch back to with fullscreen or borderless.
Sorry for some reason i can't upload my screenshots...
Yes, my friend did this for his steam deck and it worked.
For my steam deck, there is something strange. When it changes to the gamepad layout, there no option to actually use the ID, just read it. We manage to multiplay though (my friends layout didnt change, so hi used my ID). But I cant do this by my own.