Check out linuxdeploy-plugin-conda
Maybe you are interested in https://github.com/TheAssassin/linuxdeploy-plugin-conda#example which could potentially simplify AppImage generation from Conda packages a lot.
@probonopd thanks for the information. Actually our script to create the appimage is pretty simple, but includes some manually steps (removing unnecessary stuff, some workarounds...) It can be found here: https://github.com/FreeCAD/FreeCAD-AppImage/blob/master/conda/conda.sh
We use this now for several months to make py3/qt5 builds of freecad available. I am very happy with this solution as it is very simple compared to using conda directly...
Fun fact: the idea to make a conda plugin was partially inspired by you using miniconda.