I've just been reading that 10 out the top 20 mens players (including Thiem, Zverev and Berrettini) are down to play in Kitzbühel, Austria. Which starts on the 8th of September, I think (half way through the US Open).
So, either this means these players are showing intent that they aren't going to the US, or are hedging their bets, and trying to do both (if they lose early early enough, and quarnatine laws allow- they will make it to Austria?).
This is what the ATP site article says-
'To be eligible to compete in the 28-player Kitzbühel singles main draw, Top 10 players (as of 3 August 2020) must have competed and lost at the US Open — singles or doubles — by the start of the qualifying competition or by 7 September, whichever is earlier. All other players who are still playing at the Grand Slam championship will be withdrawn at this deadline. The doubles field will include 16 teams.'
Bit of a headache, again, for whoever is in charge.