I hope that Mihoyo eventually follows with the rest of their catalogue as well - though for them they only have Honkai Impact 3rd on Steam.

That is because their focus is not Steam but Epic, and on Steam does not necessarily mean it's playable under Linux. Is Destiny 2 playable on Linux? No.

Honkai Impact 3rd was the one that needs the most effort to play on Linux. Honkai Star Rail is the second since it uses ACE as well.

However, your news seems to be a bit behind. Since Patch 3.8 of Genshin OS servers, anyone with Proton or Proton-GE could enter the game using the official launcher without any additional anti-cheat patching effort, without any "Steam Deck only" device limitations like some other Gatcha games like Infinity Nikki, Mecha Break, STRINOVA etc.

And for their Zenless Zone Zero? Well, the above took place on DAY 1 of their 1.0 public testing. Enter Heroic, download their launcher, select proton or proton ge, run the launcher, install the game, and you are all set.

In terms of time, Genshin does this earlier than Wuwa. In terms of time relative to public testing, ZZZ does this earlier than Wuwa. So it's not Mihoyo follows them, it's them following Mihoyo.