I would take it as a rumor, personally.
The gold reserves of the United States has been a particularly controversial topic through the years for obvious reasons. And talking about using a significant amount of them to buy an asset like Bitcoin will definitely find opposition from the democrat party (which harbors much anti-decentralization sentiments).
It would be more realistic if Trump managed to pass a law which used seized Bitcoin from illegal activities to start to stockpile their own Bitcoin reserve for the ground up.
Even that law would find some level of opposition from the democrat party.
Isn't gold decentralized? They oppose bitcoin because it is too unstable, easily manipulated, uncertain...not because of its decentralized and uncontrollable.
Overall: there is a lot of noise around the US selling gold to buy bitcoin. But you're right, it's all just rumors so far. Senator Lummis initiated the idea, but she herself never stood up and called for and formed a group of supporters to discuss and propose the idea to Congress. As long as it hasn't happened, it's all considered unreliable rumors.