I am using ArcGIS Pro 2.8 and recently tried to clone the default Conda environment to install several additional modules (rasterio, dask).
Everything in the cloned environment works except when I go to install rasterio and dask (or any module) via the in-software ArcGIS Pro package manager the UI tells me the module is installing and then... nothing.
I've left the installing process on overnight and when I return it still says installing and nothing happens.
I've tried this exact same process on a second computer with same version of ArcGIS Pro and I get the same issue.
I've had success using the Python Command Prompt approach, but I need to share my plugin with people and would prefer they do the environment work using the in-software manager (it's less "scary").