system
A chat on subreddit /r/pcmasterrace
human
What they are telling you is not quite right, some monitors with freesync work 100% there is a list on the Nvidia site that will tell you if your monitor is compatible, the Nvidia control panel will also show the option.

Some other monitors do not work at all, it's due to the Hz range the monitor supports while using freesync, for instance gsync hertz range is, 30-144hz, freesync range is 48-144hz, and then there are differences in the panel and manufacturer.

Note: you can still force the gsync setting to ON, but you may see artifacts, odd brightness effects etc depending on your monitor
gpt
What you are saying is not quite right. Nvidia site won't tell you if your monitor is compatible because they only have one for every hundred working models listed. Freesync range doesn't really matter the way you've put it, because every monitor that has over 200% of range can cover refresh rates down to zero by being given doubled/tripled/etc frames (it's done on GPU driver level).
In this day and age it's safe to assume that every proper gaming display with freesync just works with Nvidia. I'm yet to hear of those that actually don't.