Thank you SOOO MUCH! I’ve been working on this for days and was going to return my new phone! I didn’t realize that my calendar is not an iCloud calendar, it’s Gmail and this was the answer! I’ve tried everything that everyone else said and yours hit the jackpot! I cannot thank you enough! This was your fix:
Settings>Mail>Account (select the correct account)>Calendar
then toggle OFF calendar. It asks if you want to delete the account and you accept. After about a minute, toggle it back on, and the calendar entries will start repopulating, and the search function will start working. Depending on how many calendar entries you have, it will take a while to update, but I have thousands and it updated in less than one hour. Search function works again.