Try the attached file. The zipped file has both graphicscards.sgr and graphicsrules.sgr these files will help the game recognize the card.
The GTX920MX is rated for medium settings.
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The files in the zipped file attached should work. Download and unzip. You can overwrite the current .sgr files with these. - Delete or overwrite the old graphic files with the new ones.
1. Take the zipped file from the post and copy to
C:\Games\Electronic Arts\The Sims 3\Base Game\Game\Bin
2. Unzip it and overwrite what's there, it's fine this is to help get the game to recognize the graphics card.
3. You may need to load the game to main menu and exit to make the Config.log file be aware of the change.
4. The Config.log file should be able to say "Found: 1, Matched: 1" After this, the game should recognize the game.
-- To unzip (extract) files or folders from a zipped folder, locate the zipped folder that you want to unzip (extract) files or folders from. To unzip all the contents of the zipped folder, right-click the folder, select Extract All.