The "Launcher" might require you to enter credentials to "validate" the DLC, which can lead to stolen account information.
If playing on Linux/Steam Deck, you must add the game to Steam via this specific Launcher.exe , as running RDR2.exe directly will often fail. Linux/Proton Specifics:
: Windows Defender often automatically deletes this file, causing the game to fail to launch or throw an "unknown error FFFFFFFF".