calendar is missing

Hello, on my iPhone iOS17, I use Apple Calendar app. In the settings, I also have Outlook Exchange slider turned on for Calendar, but I do not use Outlook app.

In Apple Notes, I wanted to remove Outlook folder category, so in Settings, I went to Notes > Accounts > delete Outlook account in Apple Notes.

Now my Calendar has most appointments missing. How do I get them back?

On my PC, I went to the same Microsoft Work account in Outlook 365 desktop app, logged into same outlook/MS account I used in my Apple Calendar, and it shows nothing. For thoroughness, I checked my other personal MS account with the same name, I checked the calendar, and it had nothing.

If the calendar appointments are not stored in the cloud, does that mean they were only stored in my iPhone? That seems unlikely.

Tomorrow I will be restoring my iPhone from backup created 1 day prior to this incident, to see if the calendar data was only stored in the device.

What caused this issue? It doesn't make sense to me. It seems unlikely that calendar data would be only stored on the phone, everything is on the cloud today, it seems likely it would be stored in the cloud, but then why is it not there?

I have dozens of clients' data stored in my calendar data, and it will destoy relationships with clients if I cannot recover this data, please help!