When I sign up to create new site with a mapped domain,

the plans page allows the selection of the Free plan but domain mapping isn't available on that plan, so it shouldn't be a choice.

When I continue with the Free plan I am asked to purchase a Premium plan after signing up which matches the behavior when mapping a domain from a free account, so that's fine.
refs #11937
Confirmed this is still an issue:

Fixed in #22430
Most helpful comment
Fixed in #22430