Calendar freezes on iOS 18

For me, I determined it was my Exchange account that was causing the issue (my employer recently changed their security rules and doesn't allow Apple apps like Calendar to pull data). I couldn't even delete the Exchange account (Apps -> Mail -> Mail Accounts) - it showed up gray and unauthorized and didn't do anything when I tried to delete it. I had to go into accounts (Apps -> Mail -> Mail Accounts) and change the Fetch New Data on the Exchange account from Push to Fetch. This let me delete the Exchange account and that fixed the problem. It seems the Calendar was stuck in a mode of trying to continuously Push communicate with my Exchange account but not getting the response it needed, so it froze my calendar and killed my battery through background utilization. I now have to use Outlook (and its calendar and contacts) instead of the Apple version for my Exchange data (not ideal, as I did like having everything on one calendar). Good luck!