"Adobe sign-in app that my annual CC subscription was real and I had the right to use the software. How long will that last? Is there not an offline version of the software that I can run?"
Lightroom Classic can run offline just fine. It only needs to check the license once a month if you pay monthly, and once every three months if you pay annually.
"The other challenge is that LR wants to never-endingly update my presets to xmp every time I launch - so annoying!"
That sounds like your develop presets folder is locked, so Lightroom Classic cannot rename the old .lrtemplate presets after it has upgraded them to .xmp presets.
-- Johan W. Elzenga