Yes on the TV. When you browse your DLNA media then navigate to e.g. a file structure, by folder->my movies->08-dec-2020 (as an example folder structure) this can not be added to the home screen or quick access (http://kr.eguide.lgappstv.com/manual/w17/atsc/Contents/control/magicnumber_k_u_b/enga/w35__control__magicnumber_k_u_b__enga.html), which would be useful for navigating back to the folder instead of going through many clicks.
To access media in DLNA I first need to go in to the gallery app.
Your TV has a very different looking UI. Maybe they have added a few features too?
UPNP and DLNA work ok, they are pretty much the same thing, DLNA is a newer version with some improvements I believe. LG only needed to implement DLNA for both to work, its lazy.
As you see many people on the thread would like access to network shares via the other standards and protocols (samaba), nothing fancy. Apparently WebOS is based off of linux so it should be really easy to implement.
I can't comment on the slow downs from using DLNA myself as I've not experienced them. I've heard of DLNA slowing NAS drives down. Whether its from indexing massive libraries or other functions I'm not sure. What I have had though is DLNA disappearing sometimes and reappearing randomly - sometimes I turn the TV on and it's just not there, my other devices can see it. Like you said there's no need/way to configure it, it just appears! This is good and bad, good for ease of use, bad if your TV doesn't see your device, IMO they should give us both options.
Anyway Nice TV, enjoy it and Welcome! 🙂