Probably doesn’t help your problem but for folks using the Panda Touch AND an I2C device, has BTT pre-configured their device for a particular device which they specify or something different?
My inclination is to think everything is preconfigured so you have a graphical template of the gauge, just waiting to be populated with the appropriate data.
It depends on whose AHT21 you buy. It looks like you can use Grove or Stemma/QT (JST PH)