I just did this for itch dot io. Not the others.

I used a program called Lutris, which is available in the Discovery Store. Download Lutris from the discovery store and it installs to Games on your application launcher, the Steam icon on the taskbar all the way to the left.

From there, open up Lutris. You might see some update screens, just let it run.

Now you have to add itch to Lutris. So:

In Lutris, press the + button in the upper left corner, select the first option and type in ‘itch.io’ (minus the '), select it and it installs the itch launcher into Lutris. Make sure to tick the box that says ‘make desktop shortcut’, you’ll need that.

You’ll get a bunch of installation screens, when that’s done you’ll get a ‘launch’ option but just ignore it and close out of everything.

This process will put a desktop icon for itch. It looks like a blank sheet of paper.

Right click on that, and select ‘add to Steam’. Now it’s a non-Steam game you can access from Game Mode just like any other game. You can delete that shortcut now if you want.

And that’s it.

That might sound laborious and all but it’s really simple. The hardest part is waiting for all the download/installation/configuration stuff to run.

In Game Mode just launch itch like any other game and you get the itch launcher and log into your account. From here you can install and update your itch games.

One thing to bear in mind is that itch installs your games but uses Wine, so they install on the c:\\ drive, which is hidden. So make sure you note where itch is installing your games so when you go to desktop to add your itch games as non-Steam games, you’ll need to tick ‘show hidden files’ and then just navigate to the subfolder where the .exe file is. All your itch games will be in that subfolder. This works just like Windows, if that helps.

Since the subfolder with all your games is like 6 subfolders deep, you can right click on that subfolder and make a desktop shortcut for it, so when you want to add a game that shortcut will take you directly to the itch games subfolder. All your itch games install to that one subfolder so the shortcut is super handy.

I’ve installed about 60 itch games this way. They all run perfectly but make sure you use Glorious Eggroll as compatibility.

Sorry this was so long.