I noticed that in the Firewall rules there is something called mDNS so I unchecked it from having internet access. Reminds me of the mDNSResponder.exe that came bundled with the Bonjour service when you install iTunes that is used to send Apple info about how you use your PC Is this something critical for the OS or is it used for telemetry purposes to send info to Microsoft?
I don't think it is about telemetry. The reason you have it in your Firewall is becaue you either install iTunes in the past which included Bonjour or you have Ubuntu bash on your Windows 10 enabled.
no man that entry is there on a fresh install with 0 software installed so I wanted to know what it does or am I wrong in disabling it?
You can check the ISO you use to do the clean install perhaps it has Windows sub-system for Linux file in it. Either way I still don't think it's about telemetry. If you are not comfortable with the protocol all rather feature it is good you block it.
Linux processes do not have firewall entries since you can't block or allow them using the Firewall (yet). The rule properties show the dnscache (C:\WINDOWS\System32\dnsrslvr.dll) as the "mdns" firewall rule... btw, blocking DNS is probably a bad idea.