Problem with GTA IV

meanwhile i see requirements is:

Requirements

.NET Framework 4.7.2 (Should be installed on every Windows 10 machine) 

so…install

dotnet48 with winetricks to the wineprefix where you have GTA IV installed, if not sure how see this little example script called tricks.sh change variables to your paths and TRICKS to desirable dotnet48

Basically you should just run that in terminal, but put your path instead those $VARIABLES:

env WINEPREFIX="$PREFIX" WINE="$LOADER" WINESERVER="$SERVER" winetricks "dotnet48"

Then try running downgrader again, hopefully it will help