Question FreeSync won't let me go fullscreen in certain applications

[harley27]

Hello, I recently bought this monitor: https://www.amazon.co.uk/gp/product/B074JDKN3Q/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1 and it comes with amd freesync.. it also uses HDMI for 240hz. some games work in fullscreen, and some don't.. it also doesnt allow me to go fullscreen in youtube & netflix without the screen going black, my graphics driver is up to date, so is my monitor driver. I do use 2 monitors.. this is my other one: https://www.currys.co.uk/gbuk/computing/pc-monitors/pc-monitors/acer-kg271-full-hd-27-led-monitor-black-10164659-pdt.html they are both 1080p but one is 240hz and one is 75hz, your help is very much appreciated! thanks