bug: Setting ion-datetime value does not update selected day

Prerequisites

• I have read the Contributing Guidelines.
• I agree to follow the Code of Conduct.
• I have searched for existing issues that already report this problem, without success.

Ionic Framework Version

• v4.x
• v5.x
• v6.x
• Nightly

Current Behavior

When setting the value of an ion-datetime in a setTimeout, the display date updates, but after opening the datetime, the selected day does not display.

Expected Behavior

After setting the value of a ion-datetime, the selected day should also update.

Steps to Reproduce

1. Have an ion-datetime (example uses ion-datetime-button)
2. Update the value after a few seconds
3. Open the date picker
4. Observe: The new value does not show as the selected day
5. Expected: The new value would display as the highlighted/selected day

Code Reproduction URL

https://stackblitz.com/edit/angular-ramjpp?file=src%2Fapp%2Fexample.component.html,src%2Fapp%2Fexample.component.ts

Ionic Info

N/A

[aktivdigital-frontend]

@liamdebeasi Highlight is OK, thanks, but the picker show the current month, not the set month. This issue is only partially finished.

[sean-perkins]

@aktivdigital-frontend thanks for reporting this issue. I am seeing the same behavior as well.

The datetime has internal logic that requires the date be active & that we should highlight the day: https://github.com/ionic-team/ionic-framework/blob/436a8ce50847d26f8fb63ce64ea85be6f5c0bc8e/core/src/components/datetime/datetime.tsx#L1927

highlightActiveParts is unfortunately never set when the value is dynamically changed, so the day will never show as selected unless the user manually taps the day again.