OK, so I think you may be able to do much better with the lampshade. Not so sure about more complex shapes, but the lamp shades looks like it is fitted together from 6 pieces lying flat on the build plate.
When you print from the handy app but change the filament, it will just use the filament defaults, no matter if they are good or bad for what you want to achieve and better transparency is a bit special. You will definetly want to get used to Bambu Studio and/or Orca when printing transparent.
There are a few threads, but I think the most interesting one for you may be this one:
What I would suggest for the lampshade (if it is indeed just flat on the build plate) is:
In the Filament settings: set the bed temps to just below the softening temp, nozzle temp throughout close to the max temp of the filament, enable “wipe while retracting” in the setting overrides, maybe even reduce/cut cooling.
In Quality:
Use a very high layer height, set all line widths to the same width/larger than the nozzle diameter (PETG does not like too large widths, but flat transparency is a special case)
In Strength:
Set walls to 999 in order to eliminate alternating infill patterns.
In Speed:
Reduce all printing speeds to below 100
Note however that while I do hope that this helps with the lampshade, these settings will result in very bad bridging and overhang performance.
But first you need to decide if you can achieve the kind of transparency you want to get. It is quite possible that expectations just can not be met with the current level of tech. But that depends as much on the tech as it does on the expectation.