Genki still contains a lot of artificially simplified examples (but so does any textbook and that probably is no surprise).

IMO the biggest thing that feels out-of-date in Genki is the exaggerated gender-specific way that sentence-ending particles are used. That's still very common in scripted fiction. Sometimes this leads to really awkward misunderstandings. For example のよ is demonstrated as "softly feminine" in Genki, but it tends to be a lot more pointed - "that's what I'm telling you!" in unscripted speech.

I don't think it's explicitly explained that way. It's just that women sometimes talk a little like Sailor Moon characters without warning.

Once you're good enough to read authentic Japanese, it's reasonably easy to identify these misconceptions and that will tell you what you should and shouldn't imitate. (It's also really good knowledge for literary appreciation. For example, the more traditional characters in Little Witch Academia use old-fashioned women's language way more often than the new-guard do.)

People who learn from anime are vulnerable to exactly the same issues. The root cause is that fictional language is slightly different from spoken language.

However the bottom line is that it's a non-issue. The differences are small and as a beginner you don't need to be picky yet.