I installed TrueNAS Scale last month and spent a lot of time to add some apps to suit my need.
Is there a way to bind the webdav port 8081 to a domain like <name>.duckdns.org without port number?
I do not want to have the port number 8081 behind the domain name in order to access the webdav.
In general? No, of course there isn't. For better or for worse, when the World Wide Web was invented, rather than using something like SRV records to derive an IP:PORT, quick-and-easy pragmatic choices of defaulting to port 80, and adding "www." on the front to avoid collisions with DNS where the "top-level" needed an A for other reasons were selected. We are still crippled by these bad design choices a quarter of a century later, even though the browser manufacturers are trying to band-aid the ugly bits by hiding "www." in the browser bar, etc.
Now, for some very specific uses, such as CalDAV/CardDAV, some clients actually do implement SRV lookups, but this is a bit twitchy and not something you can rely on, in my experience. Where this has been done, indeed you can place an appropriate SRV record in the DNS and not have to specify :port OR www. but you'd have to see if your client application is capable of SRV lookups.
