To end the discussion here, this ended up being an ONT problem.
Apparently, the data port was corrupted? After the technician came out and recognized that the IP/DCHP were not refreshing, he was able to get it to work for an hour or so.
He came back again later after the issue returned, replaced the ONT, and this has been running smoothly since. Woof.
"First thing to check is that wifi is actually turned on. Yeah it sounds crazy but check that first. "
After troubleshooting for days, and having no wifi for weeks, this ended up being the problem. I must've inadvertently disabled it, at some point. (I got by without the wifi by daisy-chaining a mesh router to my Verizon one; it worked because I did have ethernet). Thanks for the tips!
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