Keep cool tuskegee, tearing your hair out gets you nowhere.
Your files.sfs file for sure isn't 4,35 GB in size. That'd be the size of your IL-2 DVD.
Your files.sfs file has a size of roughly 32 MB. Look into your IL-2 4.12.1 game folder, watch out for a file called "files.sfs" and right click on that file, then select "properties" and note the "size" value reported.
Next is the game installation.
You said your game is 4.11.1m.
I get it that you purchased a direct2drive version of the game.
If so, in order to have a working game installation with any Modact, HSFX, Ultrapack, DBW or the like, you need this:
Direct 2 Drive Patch for all versionsI repeat:
If your game is a Direct2Drive purchased game (and the fact that you said your game is 4.11.1m points into that direction), you need the above mentioned patch. You'll need it each and every time you wanna mod your game. (On a sidenote: If it isn't a D2D game the patch doesn't hurt either)
One you got beyond this issue, proceed installint official patch 4.12m.
Start your game to check whether it's running fine.
Next install the official patch 4.12.1m.
Start your game again to check whether it's running fine.
Next install Modact 5.20.
If you have issues downloading the files, I recommend either to use the 100MB Chunks from Mediafire or the Torrent provided in the same post:
https://www.sas1946.com/main/index.php/topic,36163.msg396275.html#msg396275Best regards - Mike