Originally (maybe over a year ago) I had similar issues. But now Zitadel is one `enable = true;` option[1] away and in the official nixpkgs repo so you shouldn't really have this issue anymore. I was able to use it pretty easily with the built in service and postgres service[2] (note mine is encapsulated in a nixos container but otherwise the inner config is all you really need).

[1]: https://search.nixos.org/options?channel=25.05&query=zitadel

[2]: https://git.joshuabell.xyz/ringofstorms/dotfiles/src/branch/...