Here's the deal ... Rowland was supposed to cohost the popular NBC morning show alongside Hoda Kotb Thursday after being interviewed about her new film "Mea Culpa" when she dropped out at the last minute.

Page Six says sources told them she left because her dressing room wasn't up to snuff. Rita Ora filled in, and the show went on just as planned ... but, Frankel couldn't help herself when she heard the news and filmed a TikTok about the whole situation.

BF started out by saying Kelly's right ... the dressing rooms are tiny, the catering's awful and the makeup area is communal -- before adding none of that matters.

Frankel called the show an "institution in entertainment" and said it's an honor to even be there alongside Hoda ... before ending by saying it was not the moment for "diva expectations."

BTW ... some fans online are pointing out Bethenny did something similar in the past -- posting her own video about the backstage area of "Today" ... though even in that clip Frankel reiterated how grateful she was just to be on the show.

Bethenny's since taken down her video ... deleting it from her social media accounts, and she's taking a lot of heat online over calling out the former Destiny's Child star.

Unclear if Rowland's caught wind of Bethenny's comments ... she hasn't said anything about walking off "Today" as far as we can tell.