If the app requires an internet connection I’d recommend to stop using it and just use the built in print dialog. The printer shouldn’t need constant internet connection, just a Lan connection where it can broadcast on. The printer may have to connect sometimes, for which I’d recommend Ubiquity’s mobile router, easy to manage, runs on usbc, but it is a bit pricy.

A teardrop attack likely won’t “breach” the firewall, it’s just a denial of derive meant to kick your network offline. Turn your modem off for an hour, check it works once it’s back on and otherwise call your ISP to get a new IP.

IRC, it’s ancient which may sound bad but it means that most implementations have grown mature and won’t cause issues.