Dynamic DNS – Dynu.com
https://www.youtube.com/watch?v=wCJjiHp0d0w use that
https://www.youtube.com/watch?v=ZKEGP_qBmxg and this to fill the gaps.
https://www.dynu.com/DynamicDNS/IPUpdateClient/RaspberryPi-Dynamic-DNS specific to pi
Unable to get the router port forwarding to work. I may need them to “upgrade” the service by undoing whatever they’ve done to make it not work!