There are a few reasons you may be getting that error message.
First, it looks like there's a typo in the installation command: you've written
conda install -c condo-forge deicode
but the correct command should be
conda install -c conda-forge deicode
(note the "a" in "conda-forge").
If you're still getting a no plugin/command named 'deicode' error message from QIIME 2 after trying that second command, I would suggest running qiime dev refresh-cache before attempting to run the qiime deicode rpca ... command. That might fix that problem.
If things still aren't working out, let us know and we can look into this further! :qiime2:
Thanks for sharing this screenshot! It looks like you've installed DEICODE into your "base" conda environment (see the (base) off to the left side of the screen?) -- the problem with doing this is that you won't be able to use this installation of DEICODE from within your qiime2-2020.2 environment. These environments are separated from each other -- this is also why, for example, we can't use qiime commands from outside of QIIME 2 environments. Does that make sense?
So: could you try activating your QIIME 2 conda environment and then running conda install -c conda-forge deicode? I think that should solve this problem.
I was able to understand your advise.
I am glad to inform you that problem is now solved !
I am very grateful to you for your help!
Thank you very much!