Was the homosexuality angle added in It Chapter Two after the "gay Pennywise" drama?

A few things. First, Pennywise is an inter-dimensional god-like entity. In the book and the second adaptation, Pennywise is 'female' in the sense that Pennywise has laid eggs to create more entities like itself. So if you want to consider Pennywise a female entity you have some basis - however, I tend to think of it as wholly different from any notion of animals/humans.

As far as homosexuality being inserted into the film - there are two obvious places where it might have been added and one of those is in the book. In the book, the brutal attack on homosexuals is the spark that lets Mike know that It is back. This is the same attack as in the film. It is a condemnation of such behaviors and the book makes it clear that It's very presence corrupts the adults in the town. They either turn blind eyes to evil or they succumb a lot quicker to it that they would otherwise.

The other place where there is homosexuality is between Richie Tozier and Eddie Kaspbrak. This is kind of forced, IMO, because it seems out of place. Perhaps not with Richie who flirts with Beverly in the movie/book but in the film he isn't seen having any adult relationships. If I recall correctly in the book he was married a few times. Eddie marries a woman that is just like his mom (in the film the same actress plays both his mom and his wife) and he's essentially controlled by her. In both the book and the film it's clear that none of the losers has remained in contact with each other, so the lingering romantic feelings that Richie has for Eddie seem to come out of nowhere unless we assume they got back together in some unseen moment. Maybe Richie is regretful about what might have been when he's thinking about those times. I'm not sure.

That's not to say that it couldn't make sense - in fact, there is some precedents with Its the behavior of making people feel evil, ugly, and wrong. So, for example, it could make sense that It was influencing Richie his entire life to suppress his homosexuality (or just his feelings for Eddie, if Richie is bi or what have you), but I can't recall It ever directly referring to that for Richie - I could be wrong though, he might have said something about having a secret, my point though is that, to stay consistent, it would have been overly in your face, for Pennywise.

The opening scene of the movie was taken almost scene-for-scene from the book, so that was King's original invention.

According to the producer, the homosexuality of the characters was added because of how they read a scene in the book and there is no explicit mention of reacting to the internet's viewing of the first movie (spoilers):

Barbara Muschietti told IGN that there was one key Richie and Eddie moment from the book that stuck with her over the years: "The scene of Eddie's death, when Richie is saying goodbye, and caresses his cheek stuck with me for a good, what, 30 years. The way I interpreted it was that there was love there. I don't know if romantic, I don't know. But it feels totally natural that it would be unrequited love. To me, when Andy presented it as a possibility, it felt very natural."