I understand where you come from, but I'd say they've made a good job of simplfying as much as they could at this early stage.
Use DNS over HTTPS for:
1. Firefox.
2. Intra app on Android phones below version 9.
3. Clouflared on Linux.
4. Their official iOS app.
Use DNS over TLS for:
1. Android 9 and above.
2. Knot or Stubby or unbound clients on Linux.
IPv6 and IPv4 are for DHCP provided DNS:
1. With IPv4, you'd need to link your client-ip (public IP of your router) with your nextdns setup.
2. IPv6 doesn't require any such linked-ip acrobatics.
Re: VPN:
If you use DNS over HTTPS on Android or iOS, you won't be able to use a VPN, and that's because the DNS traffic is itself routed through a VPN and one can't chain VPNs on Android just yet. Other than that, VPN should work with rest of the setup mechanisms.
Use DNS over HTTPS for:
1. Firefox.
2. Intra app on Android phones below version 9.
3. Clouflared on Linux.
4. Their official iOS app.
Use DNS over TLS for:
1. Android 9 and above.
2. Knot or Stubby or unbound clients on Linux.
IPv6 and IPv4 are for DHCP provided DNS:
1. With IPv4, you'd need to link your client-ip (public IP of your router) with your nextdns setup.
2. IPv6 doesn't require any such linked-ip acrobatics.
Re: VPN:
If you use DNS over HTTPS on Android or iOS, you won't be able to use a VPN, and that's because the DNS traffic is itself routed through a VPN and one can't chain VPNs on Android just yet. Other than that, VPN should work with rest of the setup mechanisms.