Using classic Outlook for Windows in educational settings
Some nice guy named Brian replied from Microsoft with a bunch of questions, as per normal, I told him I have been doing computer networking for over 30 years, and I diagnosed the issue as only affecting live.com accounts on my systems. My Hotmail accounts are still working fine. It's not an issue with operating systems, etc. I never heard back from him after that, Microsoft broke this, so they need to own it and fix it.
I'm glad to see I'm not the only one having this issue, and that I'm not losing my mind. Well...not losing my mind in the sense that it's an error on my end...but I am losing my mind because it is such a basic but necessary element of email communication! Clearly, Microsoft has messed something up here. Hopefully they get it fixed soon!