Just last week, Hollow Knight got a bit of a visual and performance upgrade, as shown at the Nintendo Partner Direct. While this extends to other platforms, like the PS5 version, you might want to wait before claiming it for free via PlayStation Extra or Premium.
As per PlayStation Lifestyle, you might want to check your PlayStation library before you go ahead and claim Hollow Knight via your PS Plus subscription. Essentially, when you claim a game via the game catalogue on Extra or Premium, no matter if you had previously claimed it via Essential's free monthly games, it disappears once downloaded via the game catalogue.
Therefore, Hollow Knight fans who may have had the game installed since it was given away in November 2020 are being told to hold fire, as they may rid themselves of a permanent free license for the game. If you're not too bothered about keeping that license, then have at the new version, but otherwise we're waiting to see if PlayStation can deal with this ongoing issue, which affects a lot of user libraries without them noticing.