MPRT and FreeSync are incompatible with each other because:

• MPRT will KEEP the refresh rate at a high and constant point.
• FreeSync will CHANGE the refresh rate continuously in a range between the minimum and maximum rate of the monitor.

Therefore, all ViewSonic monitors that have MPRT(1ms) and FreeSync are not able to have both functions turned on at the same time.

As of March 9, 2021, below ViewSonic monitors that have both MPRT and FreeSync: