Heres the link: https://gtaforums.com/topic/976691-gta-iv-downgrade The install is very easy

Make sure to extract it somewhere or use the downgrade exe in your winwar or 7-zip where you installed it.

Versions of gta 4

1.0.4.0 good for enb's and has a good performance like 1.0.8.0 Downside: Episodes from liberty city is not available.

1.0.7.0 good for modding Downside: worst performance and lots of bugs
to fix the performance use either dxvk or dxwrapper
DXVK:https://github.com/doitsujin/dxvk
Dxwrapper:https://github.com/elishacloud/dxwrapper
To fix the bugs use fusionfix. Luckily when you are using the downgrader it gives you a set of mods that you want to install like colaccel,Simple Traffic Loader, and like i mentioned before fusionfix.

To install DXVK simply put d3d9.dll and dxgi.dll into your game directory and thats it.
Same goes to Dxwrapper but it has a ini file. what you need to enable are the following

DDrawCompat = 1
DDrawCompatNoProcAffinity = 1
optional: in the d3d9 section put in AntiAliasing = 1 if you want

1.0.8.0 A somewhat performance fix because it uses more ram that the last 2 versions
and rockstar fixed a bug on this patch where at the end of the game you could not climb onto a helicopter no matter how hard you tab the A or space bar button on high fps. Downside it is a little like 1.0.7.0 because sometimes the performance is not for everyone.

If you are having trouble with the option where you need to put in the specific amount of ram put in 4096. However for 1.0.7.0 users put in -Availablevidmem 2048 because 1070 doesnt support 4096.
put the command i showed you in a commandline. The downgrader should give it to you.



OPTIONALS: If you want you can use a radio downgrader to put all songs into the game if you want.

Enjoy and have fun