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I believe that dada2 taking longer on the mac isn't a QIIME2 issue. I believe it is based on the amount of threads that you can run on each computer. I looked up the CPU information that you provided. The windows has 12 available threads and the mac has 8.
If you look up the dada2 paired docs and you can see that if 0 is provided all availabe cores will be used.
--p-n-threads INTEGER The number of threads to use for multithread processing. If 0 is provided, all available cores will be used.
So since your computers have different available threads and you provided 0, dada2 is using all available cores and running faster on the one that can handle more threads.
I hope that clears things up!