I just run teleporter on my primary and manually upload that backup to my secondary. My blocklists and local DNS dont change much, so its not a big concern of mine.

Nebula-Sync and Orbital-Sync may be of interest to you. It seems like you want to automate the syncing.

Multiple Piholes?

Why do you have more than one? Is this for an enterprise-level situation?

I run unbound alongside pihole for extra privacy and I keep my unbound config in git. I have gitea set up to push out new unbound configs every time there’s a git push.

There is an iOS/macOS app called “Pi-hole Remote” that can manage multiple PiHole instances at once. I use that because it will make changes on both instances at once for me.

Other than that, I log in to each device and copy paste.

Pihole runs on dnsmasq right? Maybe you could create a cronjob to copy the underlying dnsmasq.conf to other Piholes

if you just want to have a solution where you can create / delete multiple local dns records on a raspberry, you van use terraform, it has a raspberry provider. I tried it recently, i was able to import existing records, create new ones. you just have to keep the list in a terraform project.