But I literally don't know how to go through and when i searched about its process, it doesn't work well as it said (if i understood correctly, the current qiime2 version is not compatible for picrust analysis.
And I also found that I could do this analysis on galaxy/hutlab website.
But the only concern is generating the compatible file.
If anyone knew or experienced this, please let me know how to generate the compatible files.
Or If you knew other approaches which are still working, please let me know.
That's true, but one can check which version of Qiime2 is compatible withh q2-picrust plugin and install this version in parallel with current version of qiime2. When installed as different environments, versions of qiime do not conflict with each other.
For example, I have 3 versions of qiime2 for different plugins. I run everything in the newest version and when needed, switch to different version of qiime2 and work with the same files.
Looks like you are not the only one who can not install older version of Qiime2. I was not aware of such difficulties (I managed to install older versions about a month ago. Probably something changed).
However, you still can install and run picrust2 as standalone version outside of qiime2 environment.
Just export rep-seqs as fasta and feature table as biom or tsv files (there is an exporting tutorial among qiime2 docs).