Hi @aredwan,
Thanks for providing these files.
Can you describe where you obtained your initial taxonomy file named otu_id_to_greengenes.txt ? the filename that you download from the greengenes database should be called something like gg_13_5_taxonomy so I'm wondering if you have somehow imported the wrong file.
The most updated version of QIIME 2 is currently 2019.10 with an even newer version scheduled to arrive sometime soon (in the next couple of weeks I believe). I would recommend you speak with your admin of your super computer about updating to the newest version.
Was this error like the one described here? The pre-trained classifier you downloaded from the 2019.10 version linked above was trained using a newer version of the sci-kit learn algorithm. If you can't update your qiime2 version, simply download the same classifier from an older version of Qiime2, in your case from the 2019.4 data resource page.