I'm at a hotel on their wifi and getting pounded with mDNSResponder pings and it's irritating as F*&%k to have that notification keep popping up every few seconds -- if I disable it in MacOS some of my browsing and email stops working
Incoming UDP connections are denied, if no rule exists. Instead of suppressing the notification, just make a rule. If you make a deny rule, it's the same as just suppressing the notification. If you make an allow rule, automatic discovery of computers and other resources in the local network will work (for the price of weakened security).
That's another possibility. If you just want to silence notifications for incoming connections, make a rule for them in Little Snitch. Without a rule, incoming connections are denied. So, if you make a deny-rule, the behavior is unchanged, but no notification will be shown.
I don't understand why the company is so resistant to including the option to disable notifications that people have asked for. Honestly, what purpose do these notifications serve for most users? I can't think of a single one. The only time I want Little Snitch to talk to me at all is when a program wants to make a new outgoing connection. Otherwise, it should be coded to be 100% as unobtrusive as possible.
There is an option: Make a rule which allows incoming connections. If you want to prevent alerts for outgoing connections, you make a rule which allows or denies the connection. Similarly, if you want to prevent notifications for incoming connections, make a rule and decide how to handle them.