[SOLVED] [NOT OFFICIAL] [RISKY] [REQUIRES SHARING SENSITIVE INFO]
Finally, after all these attempts, I managed to solve this issue. However, it involves sharing your Epic Games credentials with someone you fully trust and approving their login (if you have Two-Factor Authentication enabled).
Based on the theory I mentioned earlier—that Epic Games saves the state of a corrupted installation in the cloud—we need to force a reset of that state. I was able to do this using the following steps (assuming Epic Games is installed on your (C:) drive):
Uninstall the Epic Games Launcher.
- Delete any Epic Games-related folders located in these paths:
C:\ProgramData
C:\Users\[MyUser]\AppData\Local
C:\Users\[MyUser]\AppData\Local\Temp
C:\Users\[MyUser]\AppData\LocalLow
C:\Users\[MyUser]\AppData\Roaming
Run a search for "Epic Games" in the root directory of your (C:) drive and delete any remaining files or folders.
Ask a trusted friend who already has GTA V installed (via Epic Games) on their own PC to log out of their account and log into yours.
Reinstall the Epic Games Launcher on your PC and check the status of GTA V. After step 5, the game finally allowed me to install it properly. If this doesn't work for you right away, I suggest logging out on your PC and asking your friend to start the uninstallation of GTA V on their PC while logged into your account. This might force Epic Games to update the installation status in the cloud.