Thank you. To help "figure out what it was," is there a user-friendly software tool that can probe all ports and look for vulnerabilities by giving it my public-facing IP address?
There are many tools, however if someone downloaded a malicious email or visited a malicious link, none of the tools scanning your public IP will help you, as the threat would have been initiated by a user, not an attack on your public services.
While many tools exist, they also expect you to understand them and the risks associated with them, my suggestion would be (and it's not free), get someone to run a pen test both internal and external for you and give you a report on their findings. Use this report as your starting guide. Rinse and repeat quarterly, bi-annually or annually as needed.
If you must do it yourself, do note that you also accept the risks and consequences.
Tools like Greenbone vulnerability manager, Nessus, Qualsys, Microsoft Defender (E3 or above I believe) and many others exist.
Do also note that most of these tools are not really 'user' friendly as they are meant for IT people with experience to both understand them and know how to deal with the problems highlighted.