I use displayport connected to my rx580 with the monitor but in OSD menu the freesync is blured out and in the ands software is the same thing..It says that it isn't compatible with freesync.
Sorry for my bad english.
Applying Samsung’s advanced motion blur reduction technology to its superior VA panel, Samsung has succeeded in creating the industry’s first curved monitor CFG70 with a super-fast response time of 1ms (MPRT) that lets you enjoy unprecedented gaming performance without motion blur across the entire screen.
※ Slight flickers may occur and the FreeSync cannot be used if the fastest mode or faster mode is selected
So maybe that's the issue ? Try turning ambr down in settings and then see if freesync works.