It looks to me that this line [1] doesn't work in the scenario in which only ceph-nfs is being deployed (nfss) together with the client role (clients) but external cluster 1. https://github.com/ceph/ceph-ansible/blob/v4.0.41/roles/ceph-facts/tasks/facts.yml#L254
*** Bug 1937996 has been marked as a duplicate of this bug. ***
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 (Important: Red Hat Ceph Storage security, bug fix, and enhancement Update), 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-2021:1452