I also just had the amp replaced in my 2019 ES 350 stock radio and agree with all of Pam's comments. If you push the fader all the way to the rear one or two notches, you can adjust the sound better than before. Some may think it is a modest improvement, but I am satisfied until I can get rid of the lease.
I had to talk with several people at my dealer and even provide them the TSB number before they would acknowledge the problem. Be persistent if they stonewall you.
I have been a long-time fan of Toyota because they were a leader (perhaps THE leader) in automotive quality and fuel efficiency. This has really disappointed me. First, they put this sound system in the car apparently without field testing and then tried to defend it for over a year as a design "feature" even while they were changing the 2020 model. Why change it if was working by design? Without consumers complaining in forums like this, they probably would not have.