Not a solution to your exact problem, but when you are connected to a remote server via Dolphin you can right click anywhere in the file view and select "Add to places" (exact wording might be different) to create a shortcut.
That way I have easy access to several different drives. Webdav for my Nextcloud server, sshfs for most of the Linux machines in the house. And when we still had Windows PCs I'd access those via Samba. FTP is possible as well.
But yeah, UPNP is not aa universal as one might hope. Every time I try it with something it's buggy even on devices that supposedly support it fully. So I usually end up creating alternative access methods, like you did.