Syncing issue with my Calendars between my iPhone, iPad and my Windows 11 computer

Syncing my calendars between my iPhone (using Outlook client), iPad (using Outlook client) and my Windows 11 computer (desktop using Outlook from Office 365) has turned into a nightmare. I was using iCloud, but that resulted in duplicate calendar items on my computer that would not delete. I turned off iCloud syncing and went back to syncing through iTunes. After I turned of iCloud syncing, I brought up the device in iTunes, clicked on Info and clicked "Sync Calendars with Outlook" for both my iPhone and iPad. From there, things got worse. When I tried to sync, it wouldn't work and created new calendars in Outlook sync as "_ModCal4009.Calendar". When I tired to combine the items on this calendar with "Calendar" and then delete the "_ModCal4009.Calendar," things got worse. Now I've got most of my calendar items on my desktop while everything has disappeared from my iPhone and iPad. I'm completely at a loss. What can I do? Any help will be appreciated. Thanks!

[Re-Titled by Moderator]