There is no native way to display and email in Outlook. You could use the Outlook UI to create a new message and then type in the text, but that is a pain to automate.
If you only care about the text content, I would suggest simply using the Display message box action to show you the email text before sending it.
Alternatively, you could use scripting, such as VBscript or PowerShell to create a draft email message, review it and then make the flow send it. But it is actually quite complex to do.
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