Plug your friend's stuff. They're tired, suffering from imposter syndrome and think no one likes their work.

Really, just go on their itch page and make a tweet about one of their games. If someone does one of those "I'm looking for xyz type of game" get in those mentions and mention your friend's game. Talk about a good time you had with something your friend made.

Go on their art page and share one of your favorite pieces (if they're shareable, if not link to them and talk about how much you like it). Go tell people how much help they were on your project. Whatever, shout about your friends from the mountaintops

I've helped my friends get jobs and sales by being loud. And it's not fake I mean everything I say, because my friends are awesome and make cool shit. I bet yours are/do as well.

Furthermore, when your friend makes something they're proud of and NOT EVEN THEIR FRIENDS talk about it, that's a pretty hard hit.

And when you do talk about your friends stuff be specific. "My friend made THIS and I like THIS about it". Putting them on random lists of a bunch of creatives isn't as helpful.