Adobe have posted in 2019 saying they no this is a feature people want. https://community.adobe.com/t5/after-effects/essential-graphics-custom-font-style-italic-or-regular-or-bold-within-a-paragraph/td-p/10199219?page=1
I think in the meantime, you’ll have to provide different text layers for the different formatting.
You could probably use a form of markup to get users to denote italics:
e.g. “word [i]italic_word word ” or “word *italic_word word”
then use an expression to break up the text by these tags, but it feels a bit overkill and you’ll end up offering more support to people who don’t understand compared to just having two text boxes labeled: Book Title and Studio/Director etc…