I am satisfied with pve and qm commands on proxmox, but I wish there was a nix answer to pfsense where my network and firewall are defined declaratively
This! pfSense/OPNSense seem to me like perfect candidates for declarative configuration. Even though, technically speaking, they are since everything is being save to a config file, which you can backup and restore. It's just less declarative then you'd like it to be. Sounds like they could easily employ Nix for handling that, though.
It is a scripting language but for Mikrotiks you can scp a .rsc file and