The 2nd movie may retcon the reboot, but this shouldn't be done blatantly. But on a few occasions, blatant retcons might occur. Here are some examples I thought of.

- At the beginning of the movie, the girls are recalling the entire timespan of the franchise as a whole. One of them refers to the franchise as "an animated student film, two pilot shorts, six whole seasons, a feature-length movie, a Christmas special, two anniversary specials, and even an anime series", thus breaking the fourth wall. However, she does not mention the reboot. She'd actually deem the Chris Savino era aka the seasonal rot, the first movie which was a box office bomb, and even PPGZ canon, but not the reboot.

- This next one occurs when the professor meets Bunny for the first time. He mentions that he never created any other girls prior to creating Blossom, Bubbles and Buttercup. In short, this scene is denying that Bliss ever existed. Even further, the movie actually states Bunny to be the first purple Powerpuff Girl to exist.

Those are the only ones I really thought of. But the only problem is these might not be considered retcons but rather indications that the 2nd movie is pre-reboot in the PPG timeline. But fortunately this movie should make it clear that the reboot is officially non-canon.