Thank's for your answer.
My gog version of sins is updated to 1.921 so maybe the mod I use has not been updated to fix the problem. (this mod was release on Feb 6 2018..)
I've been able to launch a single player game by using "enter" to get past the first screen indeed.
If I click two times on "tab" then "enter" I have the multiplayer menu (haven't tried to launch a game but I got the menu^^).
I don't know if I can make a rollback of version with gog, anyway, I think I will wait for a mod update or just play original game or try local multiplayer with a friend later
PS : on sinsmodmanager v3, I found the right icon to configure sins of the fallen, 3rd line, first icon^^.