Hey @xchromosome,
It may not be possible to install it with the latest version of QIIME 2. The latest version of the plugin was written for the 2019.10 version of QIIME 2. QIIME 2 and PICRUSt2 share several dependencies and when incompatible versions are required by either this makes them impossible to install together in the same environment. When I make the next version of PICRUSt2 I'll make sure all dependency versions are compatible with the latest QIIME 2, but this will keep being an iterative process unfortunately I think.
Best,
Gavin