Roberts attempts to address this in the majority opinion:
> JUSTICE BARRETT disagrees, arguing that in a bribery prosecution, for instance, excluding “any mention” of the official act associated with the bribe “would hamstring the prosecution.” But of course the prosecutor may point to the public record to show the fact that the President performed the official act. And the prosecutor may admit evidence of what the President allegedly demanded, received, accepted, or agreed to receive or accept in return for being influenced in the performance of the act. See 18 U. S. C. §201(b)(2). What the prosecutor may not do, however, is admit testimony or private records of the President or his advisers probing the official act itself. Allowing that sort of evidence would invite the jury to inspect the President’s motivations for his official actions and to second-guess their propriety.
It seems a little contradictory ("second-guess their propriety"? isn't that the point of a bribery indictment?), but the outline is clear, I think. Prosecutors are restricted from 'probing' the act (asking for records, testimony, etc. from the executive branch) but can use all evidence they otherwise would. The official act can be mentioned. Accepting the bribe is the prohibited, unofficial act for which the president enjoys no immunity from prosecution.
> JUSTICE BARRETT disagrees, arguing that in a bribery prosecution, for instance, excluding “any mention” of the official act associated with the bribe “would hamstring the prosecution.” But of course the prosecutor may point to the public record to show the fact that the President performed the official act. And the prosecutor may admit evidence of what the President allegedly demanded, received, accepted, or agreed to receive or accept in return for being influenced in the performance of the act. See 18 U. S. C. §201(b)(2). What the prosecutor may not do, however, is admit testimony or private records of the President or his advisers probing the official act itself. Allowing that sort of evidence would invite the jury to inspect the President’s motivations for his official actions and to second-guess their propriety.
It seems a little contradictory ("second-guess their propriety"? isn't that the point of a bribery indictment?), but the outline is clear, I think. Prosecutors are restricted from 'probing' the act (asking for records, testimony, etc. from the executive branch) but can use all evidence they otherwise would. The official act can be mentioned. Accepting the bribe is the prohibited, unofficial act for which the president enjoys no immunity from prosecution.