The standalone versions of both Uncharted 4 and Uncharted: The Lost Legacy appear to have been removed from PlayStation Store in the leadup to Uncharted: Legacy of Thieves Collection.
Sony revealed the Uncharted: Legacy of Thieves PS5 release date earlier today, and soon after that users on ResetEra noticed that neither of its constituent games can currently be purchased on their own via PlayStation Store. Instead, you'll now have to pick them both up together via the Uncharted 4: A Thief's End and Uncharted: The Lost Legacy Digital Bundle for $39.99 / £34.99.
To be fair, that's the same price as both the standalone games put together, so this is likely just a move to consolidate store options; it could also be related to the fact that players can pay a one-time fee to upgrade their PS4 versions of either game to Uncharted: Legacy of Thieves Collection. Plus, you can still pick up physical copies of either game. We've reached out to Sony for more information about these apparent delistings and will update this story with any response.
Meanwhile, if you do have a PS5, it looks like it will be worth your while to play through the Legacy of Thieves Collection when it arrives in January (it's also coming to PC, though Sony's waiting until next year to share more details about that). The new-gen bundle includes three graphics modes as well as full support for DualSense haptics and adaptive triggers.
While Legacy of Thieves won't include Uncharted 4 multiplayer, Naughty Dog has confirmed it's still working on The Last of Us Factions.