But…
For the other case, “User has opted-out of Community Taxon” only for some of their observations, you can use this project to filter out observations, adding ¬_in_project=153322
in your search URL:
https://www.inaturalist.org/projects/user-has-opted-out-of-community-taxon-observation
These observations are not pushed to the yellow label projects.
But, since the staff asked me to delete my other project (at the time of their encouraging response above), I have no more technical way to avoid pushing most of the “opted-out” observations to the yellow label projects.