Hello. I have purchased a L4 license for my x86 based installation.
Everything works OK so far - except that there is no /ip cloud option.

Is this something I can install?

Found the answer. The option "ip cloud" is not supported on x86 due to the inability to verify hardware reliably. See below:

viewtopic.php?p=430762&f=2#p430762

So is there another way to implement a working DDNS service on an x86 installation?

Some third-party DDNS service with API that can be called from RouterOS (sorry, don't know any specific one), and write a script.

Dnsexit for example. Search the forum...

One of these in your LAN (as it has IP>Cloud)
https://mikrotik.com/product/RB931-2nD