Hi @Uni,
Thank you for the kind words!
Fragment placement in Greengenes2 uses an improved algorithm called DEPP. For 2022.10 we placed ~20M V4 ASVs, which can be readily used. For non V4 data, we do not yet have a means to place fragments but we are working on getting the steps described in a tutorial. For these data, one viable path forward would be to use the non-v4-16s action which performs closed reference recruitment to the backbone, and then to use the 2022.10.phylogeny.id.nwk.qza phylogeny. Alternatively, it is likely possible to train a SEPP model from the backbone, but I haven't done that before and there may be increased unknown.
More information on how the files differ can be found in the Greengenes2 tutorial and in the README with the files.
Best,
Daniel