Add a link to an email in the Calendar app

Happy new year to all!

iOS used to allow me to link to an email in a Calendar entry. It was a simple case of dragging-and-dropping the email from the Mail app into the URL field of a Calendar event. Now, whenever I try to do this, the URL never generates when dropping in.

Has this feature been removed? Is there some setting I may not have thought about that may prevent this working? Or is there a workaround?

I'm grateful for anyone taking time to read, but before responding, kindly note the following:

• I want to add a URL to a Calendar event that will link back to a target email.
• I'm not trying to create a Calendar event from a date/time in an email body.
• I'm aware you can manually create a URL using the message:// protocol and the message ID, but I cannot find a way to view the message ID that isn't extremely convoluted. If there is a quick and simple way to view a message ID on iOS, that could be a problem-solver.
• I'm aware that you can drag-and-drop emails into the Attachment field of a Calendar event, but this is no good, because Calendar on iOS cannot open Mail files.
• I've read that other apps (e.g. Airmail) allow this, but I'm not interested in using alternative apps at this time and, if possible, would like to use the Mail app .
• I'm aware that the Calendar app on Mac can often generate a link back to email automatically, but it's not always practical or possible to use my Mac.

Thank you!