HoYoverse has announced that Genshin Impact PS4 support will be ending next year, and that various functions relating to the game's PS4 version will be winding down over the next few months as well.
As revealed in an article on the HoYoverse website, support for Genshin Impact on PS4 will end on April 10th next year, at which point you'll no longer be able to log into the game on Sony's last-gen machine.
Additionally, from September 10th this year, if you've never downloaded Genshin Impact on PS4 before, you'll no longer be able to do so. If, however, you have downloaded the game on your PS4 prior to that date, you'll still be able to download it again if you wish (until April, anyway).

Following the PS4 version's delisting in September, in-game purchases will be removed from this version of Genshin Impact on February 25th next year, but if you've bought anything and have yet to claim it, you can do so until April.
Naturally, this delisting won't affect the PS5 version of Genshin Impact, nor will it have any impact (ahem) on other platforms like PC or mobile, so you'll still be able to play it everywhere else it's currently available.
As for why the game is being removed from PS4, HoYoverse says it's "due to limitations related to hardware performance and platform application size".
On what is almost certainly a related note, the studio also revealed earlier today that device specs for other versions of Genshin Impact will be raised following the next version update (which doesn't have a release date yet). It's likely the PS4 wouldn't be able to handle what HoYoverse has planned for the game in future.
This news follows the release of Genshin Impact Version 5.8 last month, which is likely to be the last 5.x update before Version 6.0, as well as the introduction of age verification for players in the US earlier this year.
For the time being, Genshin Impact is still available on PS4, and you can also download and play it for free across PS5, Xbox Series X|S, PC, and mobile devices. Stay tuned for more.