I encountered the same thing on the right rear of a Sienna with new rear pads and rotors when cold. The first go round was the dealer disassembling, cleaning and reassembling the right rear without success. The second go round was leaving it overnight so they could recreate the problem when cold. At that point the dealer suspected contaminants in the pads introduced during manufacturing. Something tells me I was not the first to have that problem. They replaced both rear pads, free of charge inside the 12 month service warranty, and they have been OK since. So that's one possibility.
I have to say if the vehicle has not been driven for several days I consider some initial scratching to be normal--2004 Sienna, 2006 Accord, 2014 Sienna, 2020 CX-5 all have done it from I presume a bit of corrosion on the rotors from sitting. Those were/are garage-kept vehicles. I suppose if parked outdoors it might show up if sitting over a shorter period. After braking when backing out of the garage then braking into the first turn all has been well with all of those vehicles.