Before iOS 13 I could view an email, select print, then 3D-touch the preview and share the email as PDF with the share sheet to my app of choice. In iOS 13 this does not work, perhaps because 3D-touch is no longer available.
Am I missing something? Is there another way to save an email as PDF in iOS 13 with the Apple mail app?
If you are using a device that still has Force Touch (like an iPhone XS), nothing has changed.
If not, you can achieve the same entering the printing dialog, then you have to do a pinch-to-zoom gesture in order to enter the PDF sharing window (or whatever else it is being called).
More on the matter at:
Yes, those instructions are old, but they work under iOS 13, or iPadOS, too.
Thanks!!! 
Pinch to zoom works. 