Note that the majority opinion forbids prosecutors from referencing the official act in court, no matter the charge. So they'd have to prove the President accepted a bribe, but never mention anything about the ambassadorship. How could a jury ever reach a guilty verdict? At most, the evidence would point to a President receiving a lavish monetary gift.

This isn't a misreading of the ruling. Justice Barret dissented from that particular part of the majority opinion, bringing up the hypothetical of bribery.