conda install
make sure you have a cloned environment active, or you will have to do a 'pip' install into the arcgispro-py3 environment
Dan:
Currently Spyder is not available from Pro's package manager GUI?
The package manager list is out of date and is showing packages for 3.9. Esri is aware of it and I only discovered it in the last 2 days of Beta 3.3. They indicated that it would be updated in the first update for 3.3. In the interim, use conda. If it is in the esri anaconda site (as I have shown) packages can be installed using conda into a clone of the arcgispro-py3 environment. I can confirm this. I can also confirm that you can pip install anything anywhere as long as you know what you might break and what won't matter if you do break it