@db_ns you could download the names and associated status directly from the IUCN checklist: The IUCN Red List of Threatened Species (the archive is downloadable here: https://hosted-datasets.gbif.org/datasets/iucn/iucn-2022-1.zip) and then you could use checklist bank to match the names to the GBIF Backbone taxonomy in one call (COL ChecklistBank API).
Note that this can also be done with the web interface: ChecklistBank.
For an overview of what you can do with checklistbank and the GBIF Species API, you can check this recorded webinar: Data Use Club practical sessions: accessing and downloading species information on Vimeo and associated links: Data Use Club Practical Session: accessing and downloading species information