Foreman introduced better bootdisk help page for types of bootdisk. However, several types are not supported in Satellite, so it's will be good to remove them from help page.
VERIFIED on sat6.10.0-21.0 the help page includes only info about the full-host and subnet images, as proposed. (see attached screenshot)
Since the problem described in this bug report should be resolved in a recent advisory, it has been closed with a resolution of ERRATA. For information on the advisory (Moderate: Satellite 6.10 Release), and where to find the updated files, follow the link below. If the solution does not work for you, open a new bug report. https://access.redhat.com/errata/RHSA-2021:4702