The author and creator of the wizarding franchise was notably absent for HBO Max's 20th Anniversary 'Return to Hogwarts' reunion special, which hit the airwaves Saturday ... just in time for the new year.

While JKR did not appear in person to mingle with the rest of the cast and crew -- including Daniel Radcliffe, Emma Watson and Rupert Grint -- she was there in spirit ... but more specifically, there in old archival footage from a couple years ago, this according to reports.

Word is, clips of J.K. from 2019 are sprinkled into the nearly 2-hour show ... where she talks about casting and the early process of turning her books into a blockbuster film. Apparently, some of the cast also talks about her, but they do it sparingly ... and mostly gloss over her.

If you're wondering what gives ... it's no secret J.K. has become persona non grata in Hollywood of late, due to comments she's made over the past year that many perceive as transphobic, remarks she' since tried clarifying time and again. Still, Radcliffe disavowed her sentiments ... drawing a firm line in the sand on where he stands on the trans community.

Now, with that in mind ... it's perhaps no surprise Rowling isn't in the HBO special, but weirdly enough -- there are slightly differing takes on why she wasn't involved ... including a report claiming she herself turned the opportunity down.

EW cites sources saying J.K. was extended an invite by HBO brass, but that she and her team felt the old footage of her would be adequate. Even more puzzling, these same sources say her transgender controversy played no part in the decision to pass on joining.

HBO Max, meanwhile, confirms they reached out to Rowling, but wound up agreeing that her old clips would suffice. It's unclear, on their end, if she turned 'em down for a new interview, or if they actually shot something with her and then ultimately scrapped it.