You’re right establishmentMeans is not supported but should be. I’ve just added it. Restart R, reinstall remotes::install_github("ropensci/rgbif"), and try again:
An unrelated thing to your question: recent versions of the package require that all queries in occ_download() be within pred calls. So “taxonKey” = 2685383 should instead be pred("taxonKey", 2685383)