It's not 0.9 seconds but Red Bull have some work to do. That being said, the track is very green and unrepresentative in FP1 and Max knows he'll be on the front row anyway with Bottas' grid penalty to there's no reason for him to turn up the engine and practice for a qualifying which will have vastly different track conditions. If there's one track where qualifying speed means nothing it's Austin. It's the ultimate tyre-eater and race pace is everything. Ferrari almost grabbed pole with Vettel in 2019 but lost 1 s/lap in race trim due to the tyres going the way of the dinosaurs within a few laps.
As for today then, Ferrari presumably run their old engines during Fridays to save on the new one so those times are unpresentative as well. As for the others, this is simply not a McLaren track and the layout is way too complicated for Checo to get a handle on it in this car the first day.