Hi @gn_wang,
Can you please provide more details. Are you not seeing any archaea at all, or just fewer than you expect?
What samples are you sequencing from?
Note: You do not need to follow all the steps from that tutorial, as it is just a set of examples, as described there. You can try skipping the rescript filter-seqs-length-by-taxon step. See this example and this example. I say this as that step might be removing sequences that you need for classification. Or, worst case scenario there are few archaea in your sample.
Have you tried GTDB or RDP? You can download both via RESCRIPt.