I try to install planemo using conda.

https://planemo.readthedocs.io/en/latest/installation.html

$ conda install -c bioconda planemo

Fetching package metadata .............
Solving package specifications:

PackageNotFoundError: Dependency missing in current osx-64 channels:

• planemo -> pyaml

Close matches found; did you mean one of these?

pyaml: pyyaml, yaml, paml

Please check this issue.