To use AMD Freesync, there're some requirement with graphics cards, graphics drivers and certified monitors.

1. A compatible GPU with a DisplayPort connection.

Compatible GPUs include all AMD Radeon™ graphics cards beginning with Radeon™ HD 7000 Series, released in 2012, and all newer Radeon consumer graphics products.Other GPUs, such as the Nvidia GeForce 10 series and newer that support DisplayPort Adaptive-Sync, are also expected to work with AMD FreeSync Technology.

For more information, please go to AMD website

https://www.amd.com/en/technologies/free-sync-faq#faq-Which-products-support-AMD-FreeSync%E2%84%A2-technology? 

2. A compatible AMD graphics driver.
AMD FreeSync™ is available using the latest AMD graphics drivers from www.amd.com/drivers.

3. A certified or compatible monitor with AMD FreeSync.

As of Nov 2, 2020, the following Viewsonic monitors are compatible with AMD FreeSync™ technology.

Please enable FreeSync in monitor's OSD menu and AMD Radeon software.

1. An example of XG2401 OSD menu where to turn on FreeSync.

2. How to enable AMD Radeon software?

Please refer to the detailed procedures in the FAQ from AMD support site.

 https://www.amd.com/en/support/kb/faq/dh-013