I have some text I was unable to mark italic so I applied 5 degrees of shear from the Character > Positioning and Transform properties. It looks fine on screen, and in an exported PNG, but I just noticed that when printed the shear was not applied and it was standing straight.
I just tested this in a blank document in both Designer and Photo and it wasn't a one-off:
Choose Artistic Text Tool
Select a typeface that doesn't have a real italic (I just tried Impact) and type some text.
Window > Text > Character > Positioning and Transform > Shear set to 5
Print (you can use Microsoft Print to PDF if you don't want to waste paper)
Windows 11, Affinity 2.1.0