Hi @zlmg2b,
Unfortunately q2-picrust2 is currently only compatible with the QIIME 2 version 2019.2 (see here for a previous example of this issue). For now, you can either install 2019.2 version of QIIME 2 (in a separate conda environment) to run q2-picrust2 with or run the stand-alone picrust2 tool outside of QIIME 2.
As for the error, I think uninstalling q2-picrust2 (and anything else that got installed with it) and refreshing the cache should get rid of that.