I recently found on Litmus previews of Outlook IOS blue text styling was happening automatically on text that could possibly be calendar event [dates, days of the week, and times]. While investigating this issue I discovered two HTML attributes I didn't know about until today [x-apple-data-detectors-type="calendar-event"] & [x-apple-data-detectors-type="link"].

The attribute reponsible for autoformatting possible calendar event text is [x-apple-data-detectors-type="calendar-event"]. The CSS present in Outlook IOS that is responsable for styling possible calendar event text is using an attribute selector plus the !important rule.

Below is the CSS responsable for the autoformatting and the solution to fix it.

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

Solution to Override Outlook IOS 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/Andriod specific selector I used to increase the CSS specificity allowing this solution to work was found here https://howtotarget.email/