The Steam Deck can't play Fortnite, Destiny 2, Genshin Impact, and a handful of other (mostly online, often free-to-play) games with anti-cheat not enabled.
It's not because it technically could not, it's because those game companies don't let it.
All the various anti-cheat things are supported by the Steam Deck. It's just a bad policy decision by the game maker to not enable it for Linux, including the Steam Deck.
To be clear: There are several f2p games and other games with anti-cheat that are enabled for the Steam Deck.
And: I do have a Steam Deck and also game ony desktop PC that runs Fedora Linux. And every game I care about (aside from Fortnite, which my nephews play) runs well.
So I basically agree, but I'm pointing out a few very small exceptions.
Red Hat didn't "close up the source" to anything. All the source to RHEL is available in CenOS Stream's git repos. All of the source to all Red Hat products is available in upstream projects too. Nothing's "closed".
What was announced was that the source to RHEL would only be publicly published in git (with history, tagged releases, etc.) instead of publically available SRPMs (unless you use a Red Hat account — even a free one — then you could also download SRPMs).