You can get it to install by temporarily editing file /etc/os-release (using sudo) and changing the line ID=osmc to ID=debian. After installing, you should change it back.
I can think of no reason why it will affect OSMC networking. It simply listens on port 53 and redirects DNS traffic over HTTPS (DoH). (As an aside, DoH is pretty insecure, which is probably why Google promotes it so much. It is known to leak data right, left and centre. DNS over TLS (DoT) is a lot more secure.)