I don't think there's any automatic fallback, but I'm not sure.
It is possible to quickly toggle on-and-off what the configuration profile sets in Settings. I've occasionally had trouble on captive wi-fi portals, like on planes, but I generally remember it's probably the DoH, so I go toggle it off, get connected, and toggle it back on.
It is possible to quickly toggle on-and-off what the configuration profile sets in Settings. I've occasionally had trouble on captive wi-fi portals, like on planes, but I generally remember it's probably the DoH, so I go toggle it off, get connected, and toggle it back on.