Considering that they are not even under oath, precisely zero. They can lie to the lawmakers' faces with no recourse.
I very distinctly remember Jack telling congress the time before last that they "do not shadowban", and then screenshots of their admin dashboard were leaked[1] that show they explicitly did have multiple kinds of shadowbans.
[1]: https://www.vice.com/en/article/jgxd3d/twitter-insider-acces...
Disregard that first sentence, apparently they are all sworn in by default. It's just that perjury is barely ever pursued.