Calendar events missing after iOS 18.2.1 update on iPhone 12

I updated to 18.2.1 this evening. The phone turned back on and everything seemed normal. A couple of hours later, I went to my Calendar app to check my upcoming appointments and they were all wiped out. In fact, events I had deleted and/or changed a year ago were now there (which was just a couple of recurring monthly events since I didn't start using Calendar much until a few months ago).

I tried all the things in the Community I've seen other people try - hiding and unhiding the different calendars; toggling off and back on the "use on this iPhone" button in the iCloud Calendar settings; deleting the Calendar Account and then re-adding/syncing it, etc. The events aren't even showing up when I search keywords in the search bar in the Calendar app (this was true when the phone first turned back on also).

Is there another option I haven't tried?

Also of note, I have had this account for a long time but I have never actually allowed my phone to sync Calendar to my iCloud, so I am wondering where this old Calendar data is being stored? There was no recovery option in iCloud! Thanks.

[Re-Titled by Moderator]