Where the SRC is one of two computers (running Windows) hooked up to the router, and DST is my IP.
Interestingly the one running macOS doesn’t seem involved.
It isn’t a configuration on your host that attracts these packets. The firewall is doing what it is supposed to do and drop unsolicited traffic. You’ve obscured the source address and destination port details, so we can only guess as to whether it is related to SNMP, Bonjour, or some other protocol. A wireshark packet capture could also be used to tell you more.
So I guess I need to either figure out how to accept the traffic
or prevent it from happening.
My first thought is that those two Windows PCs are setup to print from a common machine.
Could this be part of them constantly probing for that printer?
I don’t know much about networking. >_<
Well, I suggest posting the log entries unadulterated, so that we can at least see the destination port associated and advise further. Otherwise we can only speculate.