Popper wasn't wrong, but people today cite him out of context. His words weren't meant as a support of vaporizing people for wrongthink. (To borrow expressions from his contemporary, George Orwell).
Popper lived in a time when many far left or far right parties had well organized, sometimes massive militant wings ready to bash skulls of their opponents (think SA). He believed in restricting speech when the intolerant were on a clear path to triumph by violence, not by engaging in an argument.
But AS A LAST RESORT and in limited scope only. This is a part of Popper's philosophy of liberalism. Violence is used as a last resort only.
When you look at the case of Parler, if it was really used to coordinate the attack on the Capitol, and the digital giants decided to take it offline for that afternoon and in the proximity of the rally only (say, 100 km radius), or in a similar restricted way, it could definitely be argued that they used force as a last resort against the possibility of democracy losing control in a certain place and time.
But eternal worldwide permaban of an entire platform clearly exceeds the "last resort" test. It does not even try to be narrowly tailored to the threat, even though the giants have all the ability to do so. It is a blanket, global act meant to constrain speech of millions for actions of hundreds.
Now we can debate whether the giants should have the right to do so or not, but I think that regardless of this question, by swinging the hammer so heavily and so wide they proved that they aren't really fans of Popper-like liberalism at all. Whatever they did isn't covered by Popper's argument against intolerance as a whole.
https://fee.org/articles/why-the-paradox-of-tolerance-is-no-...