Can't point +ADD LIBRARY away from local drive C: to my NAS

A big long because I summarized several recs (many thanks to Otto Kerner and Tghowe) and responses in one place here:

I just installed PLEX Media Server on my primary computer (desktop) and am trying to set up libraries (on my NAS); I will then will add players on my HTPC and other devices. No success!

I store all my media on my NAS, a WD MyCloud EX4100 in separate PUBLIC shares for movies, music, pictures and video; all have R/W privileges for EVERYONE. I backup to the NAS from this desktop (and other devices on my home network), save videos and pictures to it, retrieve them with no problem – so absent this problem with PLEX, I have no access issues with the NAS – at least not that I’m aware of.
I tried to use +ADD LIBRARY but without success. It defaults to drive C: on the local system. When I try to change to the WDCloudEX4100 in order to select the public > movies (or music, or pictures, or video) the screen keeps popping back to my local drive C:
I have spent 2 days trying everything I can think of and have received suggestions from two forum members (with my thanks and appreciation), but am getting nowhere.
How can I successfully point the +Add Library to my NAS (wdmycloudex4100)?

Some additional background:

It was suggested that I copy the UNC address from File Explorer > Networks, however, although the WDMyCloudEX4100 was listed there since I installed it a couple of weeks ago, it is no longer listed there. I can ping the device and I can see it in my router on the same network, but it’s just not listed under Network in File Explorer. Shouldn’t matter since I typed in the UNC, i.e., \WDMYCLOUDEX4100 – and when that didn’t work I added the shares to the end of it (\WDMYCLOUDEX4100\Public\Music etc.). Typing in the IP Address and URL didn’t work either. I also mapped network drives to the public shares on the NAS (X, Y, and Z) but that hasn’t helped either.
I can get to the files in the NAS from my desktop via a link I saved to my desktop (essentially the NAS IP address), but again, +ADD LIBRARY just keeps going back to drive C: on the local system.

I also thought I could change Log On in Services from “Local System” to a user with admin privileges, however, I’m guessing that since the program isn’t yet running, all I see in Services is “Plex Update Service” – which I’m assuming won’t help with this problem.

I also checked Windows Firewall and PLEX was allowed; disabled it and the problem with +ADD LIBRARYremains. [NOTE: I haven’t used separate virus protection in the past, but thought it a good time to do so now that the Windows Firewall is disabled. I installed ESET Node32; I will suspend protection during certain operations so I don’t expect it to be a source of future problems; hope these aren’t “famous last words!”

Called Western Digital support to get help restoring the EX4100 to the listing under Network for File Explorer; no success - “…wait for level 2 on Monday.” That said, I can access all of my files on the NAS/EX4100 from each computer on my network via other means and since writing in the UNC didn’t help, it’s unclear to me that cutting and pasting that address from File Explorer will yield a different result.

Any HELP y’all can provide would be most appreciated - this retired guy has too little hair left to keep pulling it out.
thanks,
bob

you can use a UNC path with an IP address

I don’t recall the other post, so you might have already done this, but…

I don’t use my WD My Cloud for media on my server as all my media is local. I did test it on a test server on my laptop and the following works - \\ipaddress (reserved in the router)\share\media folder.
Edit Library> Add Folders>

Example:
\\192.168.1.129\Public\Movies

OttoKerner - thanks for your recommendation. Sorry about clicking no prematurely - it’s because I made the same mistake (see below) but then tried again —
IT WORKED THIS TIME! Thank you.
The mistake I was making was after putting the complete UNC in the box (as you demonstrate above) I would still click on BROWSE – a mistake - that’s what kept bringing me back to drive C: This time I clicked on NEXT and it worked like a charm.
Thanks very much - I’ll be able to sleep tonight!
Bob