I provisioned a samba-ad-dc on a raspberry pi400. Provision was successfully;
After configuration and start of named(DNS) I start samba-ad-dc and receive
this error

May 28 21:48:51 rasp samba[8051]: [2021/05/28 21:48:51.914772,  0]
../../source4/dsdb/dns/dns_update.c:85(dnsupdate_nameupdate_done)
May 28 21:48:51 rasp winbindd[8049]: [2021/05/28 21:48:51.914788,  0]
../../source3/winbindd/winbindd_cache.c:3204(initialize_winbindd_cache)
May 28 21:48:51 rasp winbindd[8049]:   initialize_winbindd_cache: clearing
cache and re-creating with version number 2
May 28 21:48:51 rasp samba[8051]:   dnsupdate_nameupdate_done: Failed DNS
update with exit code 1
May 28 21:48:51 rasp winbindd[8049]: [2021/05/28 21:48:51.975829,  0]
../../lib/util/become_daemon.c:152(daemon_ready)
May 28 21:48:51 rasp winbindd[8049]:   daemon_ready: daemon 'winbindd' finished
starting up and ready to serve connections
May 28 21:48:53 rasp smbd[8019]: [2021/05/28 21:48:53.129313,  0]
../../lib/util/become_daemon.c:152(daemon_ready)
May 28 21:48:53 rasp smbd[8019]:   daemon_ready: daemon 'smbd' finished
starting up and ready to serve connections
May 28 21:48:58 rasp samba[8029]: [2021/05/28 21:48:58.611583,  0]
../../source4/lib/tls/tlscert.c:154(tls_cert_generate)
May 28 21:48:58 rasp samba[8029]:   TLS self-signed keys generated OK

Installing python38-dnspython package solves this problem.

systemctl status samba-ad-dc output is now

Jun 09 11:31:59 rasp winbindd[23521]: [2021/06/09 11:31:59.670189,  0]
../../lib/util/become_daemon.c:152(daemon_ready)
Jun 09 11:31:59 rasp winbindd[23521]:   daemon_ready: daemon 'winbindd'
finished starting up and ready to serve connections
Jun 09 11:31:59 rasp mitkdc[23509]: [2021/06/09 11:31:59.706160,  0]
../../lib/util/util_runcmd.c:352(samba_runcmd_io_handler)
Jun 09 11:31:59 rasp mitkdc[23509]:   /usr/sbin/krb5kdc: Stash file (null) uses
DEPRECATED enctype !
Jun 09 11:31:59 rasp mitkdc[23509]: [2021/06/09 11:31:59.766003,  0]
../../lib/util/util_runcmd.c:352(samba_runcmd_io_handler)
Jun 09 11:31:59 rasp mitkdc[23509]:   /usr/sbin/krb5kdc: Stash file (null) uses
DEPRECATED enctype !
Jun 09 11:31:59 rasp mitkdc[23509]: [2021/06/09 11:31:59.776810,  0]
../../lib/util/util_runcmd.c:352(samba_runcmd_io_handler)
Jun 09 11:31:59 rasp mitkdc[23509]:   /usr/sbin/krb5kdc: krb5kdc: starting...
Jun 09 11:31:59 rasp smbd[23491]: [2021/06/09 11:31:59.913519,  0]
../../lib/util/become_daemon.c:152(daemon_ready)
Jun 09 11:31:59 rasp smbd[23491]:   daemon_ready: daemon 'smbd' finished
starting up and ready to serve connections


The packages python38-dnspython needs to be required by samba-ad-dc

Regards
Philippe