Here's how to generate a Google Calendar event from an email with event information in a browser or the Gmail mobile app.
How to Create Google Calendar Events from an Email in Gmail
If you open Gmail in a computer browser, the steps for adding a calendar event are different than when you use Gmail in a mobile app.
Open the message in Gmail and click the three dots icon on the toolbar. You can also press the period key if you have Gmail keyboard shortcuts enabled.
Select Create Event to open a Google Calendar screen. Google Calendar will populate the event name with the email subject line and the description area with the email content. Make any necessary changes in these two areas.