Use iOS shortcut to schedule an email to myself
I found I was able to do this, using the following steps.

Create a new calendar in Google Calendar (TempCal) that is set to email reminder notifications.
Link Google Account to iOS, to allow iOS Calendar app can access and edit TempCal.
Create a new shortcut, with these steps:
Adjust date - Add [time] to current event.
Add Calendar Event - Add [event name] from Adjusted Date to Adjusted Date to TempCal

When the event occurs, Google Calender emails me.
I made another shortcut to clear TempCal’s events. I set an automation to run this shortcut every evening.

Find all Calendar events when start date is in last 48 hours and Calendar is TempCal
Choose from Calendar events (select all initially and select multiple options checked)
Remove Calendar events - chosen events.