%USERPROFILE%\Documents\Arma 3 - Other Profiles\<user-id>\Saved\steam\
You can also use --eon_force_display=x command line argument on linux builds, where x is your monitor ID.
Under Steam, set command line like this : %command% --eon_force_display=0
A bug in the analytics code causes all the game threads to block during HTTPS initialization, which can cause 10-30 second freezes (the time it takes for the failed SSL connection to drop). This issue can be fixed by opting out from analytics.