API Auth has changed in V6 (see docs.pi-hole.net) - It may be that the Pi Connect app needs updating to V6 compatibility

Speaking on my own (Dan), currently no plans but that doesn't mean no full-stop. Stubby, DNSDist, traefik are made by people that know the transports/protocols versus Pi-hole including a third-party library that isn't in our control. I want anything you trust Pi-hole to do to be solidly trustable.