Not all monitors support it so if you’re not sure what it is then it’s unlikely you have it enabled but I’ll show you how to disable it just in case.
Rightclick on your desktop (on windows) and click ‘Nvidia control panel’
After a moment, a window should open that looks like this:
If it’s not already selected, select the tab on the left titled ‘Set up G-SYNC’
Then uncheck the property ‘Enable G-SYNC, G-SYNC Compatible’
A ‘Apply’ button should then appear in the bottom right of the window. Click it.
Restart Roblox Studio for changes to take effect.
If you don’t see a G-Sync related tab on the left as I do then you probably don’t have a monitor that supports it so you don’t have to worry about it being enabled, and the lag is probably coming from something else.
If you have an AMD graphics card or are using integrated graphics on an AMD CPU then you won’t have the Nvidia control panel and will need to look up how to disable FreeSync.