How to change fonts while writing an email on my iPad ?

I Have the same question - the only solution I've found is to go to Settings, Display and Brightness, Text Size and increase the font size by dragging the slider to the larger type size. This will increase the text size on all the apps that support dynamic type size, so if that's not your intent, you have to go back and decrease the font size after you send the email.

The iOS mail app editor is plain text only, with one standard font.

This is not possible in the iOS Mail app.

Sorry.