so why doesn’t she post about an amazing new plays she’s seen?
https://www.elle.com/culture/celebrities/a64459613/meghan-markle-broadway-photos-houndstooth-outfit/
"Meghan wrote, “If you get a chance to see @gypsybway, you absolutely must."
I haven't once looked at Meghan's social media since she started it back up, I'm but this wasn't hard to fine with a quick google. It probably doesn't meet your strict criteria, but tbh with media and security I can understand why she's not regularly seeing first time plays... if indeed that's the case.
I don't think there's any convincing you but my friend who works at the NT said that Meghan definitely showed interest and was somewhat knowledgable about the theatre. Again, she took that patronage and it ended because they left. You can't judge her on how in interested she was based on a patronage that ran mostly through covid, at a time when it would have been very hard for her and Harry to go to the theatre and she didn't have social media, so she couldn't rave about new plays.
But even if she hates the theatre, which there's no evidence for, that's OK. It would be nice if you're correct and it's obligatory for RF to have wide cultural interests, but that clearly isn't the case. What cultural interests in terms of theatre and ballet etc does Harry for example have?
I watched most of Suits and was a fan of the show for years before Meghan met Harry. You might not have been impressed from clips, but she was fine. She did have charisma on TV. Her acting wasn't amazing nor was it bad BUT she didn't have the type of role to showcase that. She had chemistry with her scene partners of both sexes. It was a big role - size of role, length of gig - comparatively for an actress and that can't be dismissed.