So let's try a specific example from Critical Role. Spoilers ahead for Episodes through Campaign 3 Episode 100.
In Episode 98 (Live show at the greek) the party is in a dungeon trying to thwart the plans of the BBEG, an elf archmage named Ludinus. They are looking for something he needs for his plan to release a god killing entity from one of the moons of the planet. They discover an engine powered by a demon, and end up in a fight against the demon to destory it, believing that Ludinus is after the engine.
In the middle of the combat, Ludinus, who was also in the dungeon, shows up to help them fight it. Turns out he wasn't after the engine at all, but rather somethng else. After they defeat it, Ludinus invites the party to come with him to see what he was really after, a memory storing device that would show how the gods (who he hates) destroyed the ancient floating city of Aeor (the dungeon they are now in, burried under the ice in a far north land).
The party, who all have extremely personal reasons for hating Ludinus (he's responsible for the death of one players husband and father as well as the death of two other PCs) but quickly decide to follow him anyhow instead of attacking.
They go to the memory machine, where it is revealed that the next three episodes will be a live play of the memory with a guest DM (Brennen Lee Mulligan) that the PCs will see unfold.
Now, to be fair, because it was a live show and they were running out of time before the lights got turned off, it was essential that the plot reach the point it did by the end of the show. Their schedle meant that they couldn't leave it in a natural point, and then have another session before moving on to the 3 episode mini arc (which so far is excelent, tbh). But it still felt very weird and disjointed.
IMO, the players had to be aware of the situation ahead of time, because the choice they made at the end felt very out of character for the PCs. So, while I wouldn't say scripted, it did feel pre-planned in a way that is very rare for the game. Again, IMO, I think the mistake was about trying to fit the hand-off into the live show, where they had a fixed time limit on the episode for such an important moment to the story.
And that also made it feel a bit like a railroad (again, in a way that is very rare for the game) instead of a natural progression of events. Had they started a fight with Ludinus, and he wrecked them in a couple rounds of combat before easing up and 'politely' asked them to hear him out, I would have bought it more.
All that said, a single moment like this in a campaign that overall has done an incredible job of giving players agency while telling a single story across 100+ episodes doesn't tarnish what they do, it was just very jarring for me (sitting in the audience at the Greek) when it happened. The payoff though, has definitely been worth it.