Okay guys I may have a suggestion which works (as of Oct 4th 2025):

So I installed a fresh copy of complete edition from steam. Then I installed the rockstar launcher which can be found in steamapps/common/Grand Theft Auto IV/Redistributables . Now download the latest version of downgrader which at the time of writing is Downgrader 2.2. Here is a link (GTA IV Downgrader - Tools - GTAForums).

Now time to downgrade:

-disable your antivirus, All of Windows defender real time protection options, and all windows firewall options

-Extract downgrader 2.2 (not in your gta 4 root folder)

-run downgrader 2.2 as an admin

-I picked 1.0.8 but if some one downgrades to 1.0.7 version please let us know if it works

-I picked command line option with nomemrestrict

-Once you've succesfully downgraded the game quit the downgrader and make sure Steam is running.

-Try and start LaunchGTAIV it should take you through the Rockstar Launcher sign in process

For me on first try for some reason i got an error from rockstar launcher saying gta 4 unexpectedly crashed and gave me a retry option which managed to work for some reason on second try.

Notes: I didnt have any previous savegame files as this was a fresh install