I created two text with Arial Regular and Arial italic on qgraphicsscene using setItalic function. Result is above.

When I use italic style on Arial font, the width of text increases very high, this is not normal, you can try on MS Word or with any text editor. And I didn't use bold style but text seems with bold style.

When I use other fonts when creating texts, Other fonts work right.

For Example ( I used ordinarally with Courier New and Tahoma)

I used Qt 5.13.1 and Windows.