iPhone 12, calendar events have all just disappeared.

I have used the Apple calendar for years; has been a great, simple calendar tool to have. No issues--until today. All my events, both past and future, have suddenly disappeared. Very disappointing. Have searched for an answer, tried multiple "fixes", nothing has worked. Have an iPhone 12 with iOS 18.7.1. No recent updates (cannot update to 26.5 due to large space requirement). No iCloud backup (storage full).

Can anyone help, have a miracle fix? Thx.