How to connect a subdomain from Ionos via Fritzbox + DynDNS to a virtualmin server

Hi
I’m new with this, so I need urgent help to get started.

I have set up an Ubuntu 20.04 server on a ThinkPad with static IP in my network
Installed Virtualmin.
Created a new server with a subdomain from Ionos. (subdomain.mydomain.com)
I’m behind a Fritzbox 7590 with changing IP from provider A1.

What steps are required to connect the “subdomain.mydomain.com” from Ionos to the server created with Virtualmin in the network on Thinkpad.

Hope for help and patience with a newbie.

To get web services to work with your domain (and to keep instructions as simple as possible at this juncture) you need to set the IP address of the domain to the (dynamic) IP address provided by A1

Many THX for taking care!

The steps:
1 create a noip-adress (domain.ddns.com)
2 put this “domain.ddns.com” adress as DNS in the fritzbox

OK?
How to redirect my
subdomain from Ionos. (subdomain.mydomain.com)
to this domain.ddns.com ?
Or is there another thing to do?

I know Fritzbox offers Dynamic DNS resolution / DynDNS. You could configure your system to rely on Fritzbox and keep Virtualmin out of the business of dynamic IP updates entirely - and that would work with a bit of configuration. However, Virtualmin can act as a DDNS client via Virtualmin -> Address and Networking -> Dynamic IP Updates. If you use this (in conjunction with Fritzbox DDNS or independently of it), you are likely to simplify configuration of the services that you run on Virtualmin and get logs of your IP changes within the Virtualmin ecosystem.

Virtualmin DDNS supports DynDNS and custom scripts. The latter would let you do interesting things if you have services running under Fritzbox. See https://www.virtualmin.com/node/57320

Disclaimer: my info may be dated, it has been some years since I have had to use dynamic IPs on servers.

I now have registered a mydomain.dyndnss.net

What are the next stepps??
I cannot find a guide in documentation search for DynDNS!
PS Help

As there is nobody who can or want to help me
Pls. Be so kind and recommend another forum where I can expect help!