In a grand jury, I don’t believe that they have to
That’s up to the defense at trial
Andrew Branca at legal insurrection has a lengthy piece on this case that lays this part out, but nobody here will like his conclusions as to the verdict
Perry’s comments on social media beforehand sure didn’t help
I think you meant to write that prosecutors don't have to give exculpatory evidence to a grand jury. If a prosecutor hides exculpatory evidence from a trial jury (as in the case of J6 charges), that should make a guilty verdict very shaky, and the prosecutor should be in trouble.
The linked GP article states that there is a video of Foster pointing a gun at Perry but I can't find it. In this case, if such a video existed the defense should have shown it to the trial jury. That does not mean that Perry is guilty, but the GP article is sloppy.