For a number of years we allowed Russian spy planes to fly over our nuclear bases. That ended in November 2020. In return our planes flew over their nuclear silos. It was a way to verify compliance with an arms treaty.You do NOT Know if any damage was done. Militarily that is unknown. What I do know is allowing an object to traverse our Country could pose a danger. Will it? Maybe, maybe not. The point is, it was a risk. One that made our Country appear weak at a time when we need to be showing strength.
The point being that they knew where our silos were...you can be sure they shared that with the Chinese. Knowing where they are is irrelevant. They can never get a nuclear first strike to the point where our missiles would still be there if they were to launch.
Add to that our subs would pulverize China on a full scale war.
Lastly, do you think we couldn't jam their transmissions from the balloon? I think it impossible that they gleaned anything useful from this.