It may not be a large amount of dollars for the US government, but if 70k BTC is sent to the market, it could significantly affect the price. Although Biden can formally still make decisions, I think that such decisions cannot be approved now without Trump. If it is true that the US wants to implement the idea of a bitcoin reserve, then there is no point in selling bitcoins, they need to strive to increase the amount of bitcoin. I do not believe that they have such an urgent need for money that they need to sell bitcoins for this.
It's $6.5 Billion against a market cap of approximately $1.90 Trillion. Is it still a huge amount of money? Yes. Will it hurt Bitcoin? Not really, compared to the market cap, it's a minor amount, not capable of massively impacting the price in the long-term. It'll definitely dent its price, but how long do you think it will last? The FUD deriving from the sale is what is more likely to drive the price down, as people tend to panic in such situations, thinking there's something bigger behind the U.S government selling their Bitcoin.
Bitcoin's market capitalization is over 1.9 trillion but did you know that Bitcoin's 24-hour trading volume is extremely low? Trading volume hasn't even reached $20 billion in the last 24 hours and if the US government decides to sell that much bitcoin, it will put a lot of pressure on the market. In the long run, things will recover but in the short term there will be significant impacts on bitcoin and market sentiment, which could also slow down bitcoin's price rally.
Trump isn't in the chair yet, thus, Biden can still do as he pleases for the time being. Even if the sale actually occurs, it's very likely that Trump is going to buy it back, provided that he implements his idea of a Bitcoin reserve.
Let's not forget that these are bitcoins seized from Silk Road, the government did not buy them, and it is perfectly normal for the government to sell seized assets for other uses. If it is not sold under Biden, it will be sold under Trump if the US government needs the money for other purposes.
Bitcoin Strategic Reserve? Forget it, it won't happen anytime soon because Trump and the US government have no authority over national reserves. Ask Congress and the Fed as they are the ones with authority over national reserves.