What you will need:

• A Domain you have full access to.
• A Server with a public IP Address where you can install BIND9 [Nameserver]
• A Server at the location of the desired IP Address behind the Dynamic DNS Name (e.g. a Raspberry Pi) [DynDNS Server]
• Python
• Cron

I will use “craftsmany.net” as a placeholder which you will need to replace with your domain.
“nameserver.craftsmany.net” will be the FQDN of your Nameserver you will also need to replace this. You will also need to add a NS record for “dyndns.craftsmany.net” on your main Nameservers. You can do this at you Domain registrar (e.g. Namecheap, GoDaddy, Google Domains, etc.)
“home.dyndns.craftsmany.net” will be the FQDN for your Dynamic Hostname. You can replace “home”
with whatever you want.

Nameserver

Installing necessary packages:

apt update
apt install bind9

Configuring the Dynamic DNS Zone:

vim /etc/bind/named.conf.local

Adding the Zone:

zone "dyndns.craftsmany.net." in {
  type master;
  file "/var/cache/bind/dyndns.craftsmany.net";
  allow-transfer {"none";};
  allow-update {
    key "dyndns.craftsmany.net.";
  };
};

Adding the Zone file:

vim /var/cache/bind/dyndns.craftsmany.net

$ORIGIN .
$TTL 60	; 1 minute
dyndns.craftsmany.net	IN SOA	nameserver.craftsmany.net. dns.craftsmany.net. (
				2020060209 ; serial
				21600      ; refresh (6 hours)
				3600       ; retry (1 hour)
				604800     ; expire (1 week)
				86400      ; minimum (1 day)
				)
			NS	nameserver.craftsmany.net.
$ORIGIN dyndns.craftsmany.net.

DynDNS Server

Installing necessary packages:

apt update
apt install bind9-utils

Adding working directory:

mkdir /etc/dyndns/
cd /etc/dyndns/

Generating the authentication keys:

dnssec-keygen -a HMAC-MD5 -b 512 -n HOST dyndns.craftsmany.net

You will get a key and private file like:

Kdyndns.craftsmany.net.+157+00792.key
Kdyndns.craftsmany.net.+157+00792.private

In “Kdyndns.craftsmany.net.+157+00792.private” you will find the Key which needs to be added to the Nameserver Zone:

cat /etc/dyndns/Kdyndns.craftsmany.net.+157+00792.private

Private-key-format: v1.3
Algorithm: 157 (HMAC_MD5)
Key: dMUhRv/ha86LqY7kS3k3EQjGfPDF0v3B08M0j1LPJW1l/GJv+4/Jl7G8xsDCzrq4ggq84JpCK5KFd/R2m//2hA==
Bits: AAA=
Created: 20200617134654
Publish: 20200617134654
Activate: 20200617134654

Nameserver

Adding the keys:

vim /etc/bind/named.conf.local

key "dyndns.craftsmany.net." {
  algorithm hmac-md5;
  secret "dMUhRv/ha86LqY7kS3k3EQjGfPDF0v3B08M0j1LPJW1l/GJv+4/Jl7G8xsDCzrq4ggq84JpCK5KFd/R2m//2hA==";
};

DynDNS Server

Creating the update script (If you do not have IPv6 comment out the lines with “ipv6”):

cd /etc/dyndns/

vim /etc/dyndns/update.sh

#! /bin/sh

server=nameserver.craftsmany.net
zone=dyndns.craftsmany.net
host=home
 
ipv4=$(wget -q -O - https://ipv4.info.tiekoetter.net/ip/)
ipv6=$(wget -q -O - https://ipv6.info.tiekoetter.net/ip/)

cat << EOF | nsupdate -k /etc/dyndns/Kdyndns.craftsmany.net.+157+00792.private
server $server
zone $zone.
update delete $host.$zone.
update add $host.$zone. 60 A $ipv4
update add $host.$zone. 60 AAAA $ipv6
send
EOF

Making the script executable:

chmod +x /etc/dyndns/update.sh

Adding update.sh to cron:

crontab -e

*/5 * * * * /etc/dyndns/update.sh

Verifying that everything worked:

nslookup home.dyndns.craftsmany.net

Server:		1.1.1.1
Address:	1.1.1.1#53

Non-authoritative answer:
Name:	home.dyndns.craftsmany.net
Address: 94.114.209.██

If you see the correct Address everything is working correctly.