Troubleshouting as described exactly in your Wiki https://wiki.samba.org/index.php/Troubleshooting_Samba_Domain_Members:
When joining a host to an Active Directory (AD), the net fails to update the DNS:
# net ads join -U administrator
Enter administrator's password:
Using short domain name -- SAMDOM
Joined 'M1' to dns domain 'samdom.example.com'
DNS Update for m1.samdom.example.com failed: ERROR_DNS_UPDATE_FAILED
DNS update failed: NT_STATUS_UNSUCCESSFUL
Note, that the join was successful and only the DNS updated failed.
Bug: the domain "m1.samdom.example.com" was defined as an "alias" in the DNS server.
If domain is defined as "host" in the DNS server, command executed as exspected.
FreeBSD 12.1-RELEASE-p3 #0 r360028M: Fri Apr 17 01:52:46 CEST 2020