The PC version of Red Dead Redemption does exist — this was confirmed by Rockstar itself. Interestingly, the announcement happened quite accidentally on the game's page in the PlayStation Store.
According to the description, the main features of the port will be increased resolution and frame rate, support for multiple displays, and spatial sound. Otherwise, it is the same 2023 re-release — without multiplayer, but with the Undead Nightmare DLC.
The release date of the PC version is still unknown. It is possible that the game will be released on August 17 — exactly one year after the console premiere.