Thanks for your prompt response–and for your excellent setup guide that uses pi-hole and a containerised reverse proxy! (I might end up using the approach in that guide instead, since I’m guessing the issue here is with my dnsmasq setup).
I really would like to get the local setup as defined in the main local instance/reverse documentation to work, but since it’s not as detailed as I would like, I ended up having to draw from lots of different sources to fill in the gaps. (I’m not blaming NextCloud here–they’re providing an amazing service for free, and the local setup has a more limited userbase.) If @ernolf and others can help correct the errors in these steps, we could then update the main documentation to make some of the steps more explicit.
But if that’s not possible, I may retry all this with your approach!