This is false. My NextDNS clients on macOS, iOS, and iPadOS devices all feature a Disable toggle that stops all blocking and allows un-blocked DNS resolution.
I don't use Windows at home, but I imagine there is a similar toggle.
Looks like there is a way to “pause” NextDNS. To have this ability, you have to set it up via their App and not the (recommended) configuration profile. Then you will gain a simple app with Enable/Disable toggle.