I recently found that IOS Outlook started adding blue styling to text that could be a calendar event [dates, days of the week, and times]. I discovered two HTML attributes that the commonly used IOS autoformatting fix did not cover [x-apple-data-detectors-type="calendar-event"] & [x-apple-data-detectors-type="link"].

The attribute that is autoformatting suspected calendar events is [x-apple-data-detectors-type="calendar-event"]. The CSS guilty for turning the calendar event text blue is using an attribute selector and !important so to override that styling you need to increase specificity even higher.

Below is the commonly used IOS autoformatting fix for reference. I also included the CSS added by Outlook IOS for calendar event styling and the solution to overriding the autoformat styling that occurs.

Commonly Used IOS Autoformatting Fix:
a[x-apple-data-detectors] {
color: inherit !important;
text-decoration: none !important;
font-size: inherit !important;
font-family: inherit !important;
font-weight: inherit !important;
line-height: inherit !important;

Guilty CSS Added by Outlook IOS for Calender Event Styling:
[x-apple-data-detectors-type="calendar-event"] {
color: #0072C6 !important;
-webkit-text-decoration-color: #0072C6 !important;

Solution to Override Calendar Event Styling:
body[data-outlook-cycle] [x-apple-data-detectors-type="calendar-event"] {
color: inherit !important;
-webkit-text-decoration-color: inherit !important;
text-decoration: none !important;

Note: The Outlook IOS/Android specific selector I used to increase the CSS specificity that allows this solution to work was found on https://howtotarget.email/