Would it be possible to use Dynu DDNS to allow me to RDP from my Win10 laptop to multiple Win10 Pro machines at multiple locations, all with dynamic IP? Basically I may need to manage these Windows machines all running in geographic isolation, all running dynamic IP, at minimal cost, without Windows Active Directory, and quite possibly without specific DDNS-compatible routers at the host ends. Cheers!

There is a tutorial at https://www.dynu.com/Resources/Tutorials/DynamicDNS/RemoteDesktop which you may find useful.