@Juan, Ceph tell command is working. Below is the output:

[root@magna094 ubuntu]# ceph tell mgr.magna094.hussmr help

 Tell mgr commands 
 =================
config diff                                                                                               dump diff of current config and default config
config diff get <var>                                                                                     dump diff get <field>: dump diff of current and default config setting <field>
config get <var>                                                                                          config get <field>: get the config value
config help [<var>]                                                                                       get config setting schema and descriptions

ceph tell mgr.magna094.hussmr config show

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 (Red Hat Ceph Storage 5.0 bug fix and enhancement), 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/RHBA-2021:3294