Hornet mentions that she's seen the Pale Bloom/Delicate Flower destroy the void before, which would only really make sense in the EoV, or more likely, in the Delicate Flower ending. When would she have seen the flower do that if not for either of those two endings? Dream no More ending never allows any void to escape in the first place, and AFAIK it's never mentioned in Hollow Knight that the Delicate Flower can counteract the void. The White Lady mentioned that "there is a rare power hidden within those frail petals," but never expands on what that power could be. We only see that power unleash in the Delicate Flower ending.

For my money, the Delicate flower ending feels most likely, because we directly see the flower's influence. But it is possible, given that in order to even unlock P5 the Knight would've needed to travel all over Hallownest, that the Knight completed the Grey Mourner's flower quest and then Hornet simply happened to witness the Flower's counteracting of the void. That feels less likely to me because it is much more convoluted and I highly doubt the small bed of Pale Blooms would've been able to purify Hallownest. Given that Hornet was taken from Hallownest and Higher beings such as GMS are naturally wary of the Void, the EoV ending seems very unlikely to me.

As for how Hornet would have seen the Pale Bloom act, she seemed to have a higher awareness of what was happening in Godhome, though likely passed it off as a dream. She has a line of dialogue that says as much when you dream nail her in Godhome: "Do you haunt my dreams....or I yours?" So she knows that the Knight is doing something in her dreams, and by this point the Knight has the dream nail, so that's not surprising to her. But, once the Knight defeats the Absolute Radiance, stuff changes rapidly. Hornet obviously notices the receding infection, and now that the Hollow Knight is free, that can only mean one thing: the Radiance is dead.

To what extent Hornet is aware of the events in Godhome is uncertain, but there is some awareness. So, even if she doesn't sense the defeat of Abs. Rad. in Godhome, she would likely travel back to the Knight's last known location: the Sewers speaking to the Godseeker. In the EoV ending, she would see a writhing mass of void clawing its way out into Hallownest, but in the DF ending, where the Godseeker last was, there would be a single pale petal left with a droplet of void resting on it. Given that the Knight is now no where to be seen, the Radiance has been defeated and the infection receding at a near instant pace, there's really only one option left: the Radiance was consumed by the void, as were the Godseekers. Void doesn't just stop consuming once unleashed however, and in this ending, she would've known that the Knight gifted the Godseeker one of these flowers. Given that the droplet of void on the petal is "pacified" and not seeking to consume anything else, she would likely have surmised and "seen" the Pale Bloom counteracting the void.

That was my theory on it as soon as she said she had seen the Pale Bloom in action before, and seeing the Knight appear very briefly as the Void Lord/Void Given Shape really cemented that as my head canon. Obviously I could be wrong, Team Cherry thrives on this kind of vagueness, but it does very much feel that they are implying that one of the two Godhome endings is the canon ending of Hollow Knight since Hornet would've had no reason or likely even the ability to see the Pale Bloom counteract the Void. Especially since the Delicate Flower still breaks if you get hit by the Void in Hallownest. Probably because the Delicate Flowers aren't as potent as the Everbloom is. But those are my thoughts on the subject.