Not sure how technitium works but just from my selfhosting experience are you sure your not hitting dns-rebinding protection somwhere.

In short DNS rebinding stops domains from being resolved to private IP ranges so you don’t end up back in your Network when you seem to be resolving a public domain.

I have to set up any domains that resolve locally in my router (which also does DNS and DHCP) but not sure if that’s necessary with technitium

Well everyone’s milage may vary. I have set up informant some time ago so I’m forced to read the news on updates. But much more importantly I’ve ignored .pacnew files for years till it bit me in the ass when a Pam config file change broke my login so now I’m not ignoring.pacnew but merging them every update.

Yeah that’s called “Tails” not TailOS. And it’s a pretty great tool.