All games are accessible from any device, as long as you have the correct link. The problem is that not all games support all devices.
Developers have to ability to set which platform the game supports. This information is used when choosing which games to suggest/show.
However, currently, if a link to a Godot web game that is made for desktop is clicked on mobile the game will be launched like normal.
With this feature we would add a warning message when lauching a Godot game on a platform that is not intended.