Vanessa's attempt to help Candace. She briefly went through a Cassandra stint like Candace, but gave it up much sooner. While it may not be the exact same reason (Doof's life is very hard to be envious of), she may know that Candace's desire has a subconscious reason and wants to help Candace out of a phase she went through.
During the song "Adulting", Isabella (and Ferb) strongly object to "adult" being used as a verb. "Adulting" is a very commonly-used neologism in the film's release year of 2020, but Phineas and Ferb premiered in 2007 and nearly all of its continuity takes place over a single summer — in the film's universe, it's probably still 2007, one year before the first popularized usage of "adult" as a verb.
The presence of technology contemporary to 2020 would cancel out the idea it's still 2007, though.
The reason that Baljeet's plans inspired by Space Adventure fail while Phineas's idea works just fine, is that Baljeet was trying to rely entirely on the imaginary show's Artistic License – Physics, whereas Phineas just used the show as the spark for an idea that was basically something he and Ferb do all the time anyway.
They don’t remember it to know that this is happening but in the previous Phineas and Ferb movie Across the 2nd Dimension, Phineas naïvely helped Dr. Doofenshmirtz to build his Other-Dimensionator only to be shocked after the fact by the realization that Doof was evil, which makes sense given that not only is Doof affably evil he’s in many ways similar to Phineas. Here, Candace naïvely helps Super Super Big Doctor, an affably evil character who reminds her of herself only to be shocked by the revelation that Super Super Big Doctor was Evil All Along. Like Candace said we really have “seen this all before”.
Likewise, Phineas gets rather harshly and unreasonably pushed away by Candace in this movie, just as he did to Perry in the previous one (and it could qualify as Laser-Guided Karma). And just as Phineas realized his mistake when he learned Doofenshmirtz-2 had captured Perry in the previous film, Candace realizes hers when she learns that Super Super Big Doctor has Phineas, Ferb, and their friends sent to prison (though this time it's Perry who comes to save them).
A minor example, but there's still a second chicken left on Feebla-Oot by the end of the movie, all alone.
Considering we see them in the audience before Mama begins taking over, it can be assumed that Django, Jenny, Irving, and even Isabella's fellow Fireside Girls were among the Brainwashed and Crazy crowd chasing the kids near the end.
When the portals fail to take the kids to Feebla-Oot, Baljeet claims that this was due to the planet's ion barrier making it impossible for anything to teleport on and off the planet. But if that's the case, how did Doofenshmirtz's Chicken-Replaceinator manage to work without any problems?
Perhaps it's because they work differently. Chicken-Replace-inator teleports by switching the places of the object it hit with a chicken whether nearest, farthest, Beverly Hills or Beverly Hills Adjacent. The portals on the other hand, teleport things that go though it. These are very different forms of teleportations, so it is logical to think they probably follow different laws.
They mentioned that an ion field had "formed" around the planet; it's possible that ion fields like that are temporary, like weather, and it had simply gone away by then.
Why would the Tri-State Area build a fragile statue in the outfield of a baseball stadium, where it would almost certainly get broken by a home run or foul ball?
Yes, it would, but that would be assuming that the town of idiots were thinking that far ahead.
