https://bugs.winehq.org/show_bug.cgi?id=44123
--- Comment #19 from Józef Kucia joseph.kucia@gmail.com --- (In reply to Andrew from comment #15)
Created attachment 59881 [details] Log from running 'WINEDEBUG=+dxgi,+d3d11 wine Steam.exe &>log.txt' with the MaxVersionGL key set correct;y
It doesn't seem like you set MaxVersionGL key correctly. You should see the following line in the terminal:
err:winediag:wined3d_dll_init Setting maximum allowed wined3d GL version
Try the reg file attached by Fabian.