I’ve been researching (unsuccessfully) which external HDD that is accessed wirelessly, can be used as a media storage device that works with plex. Not sure I want a full NAS, but the WD mypassport wireless pro has been discontinued. Any advice for a very casual user?
Plex will run only on a full-blown NAS device.
A mere “hard drive” won’t do.
However there is no need to look explicitly for a “wireless NAS”.
Because I am pretty certain that you already have a wireless router in your home.
Simply plug in the NAS there into a free Ethernet port. If there is no free Ethernet port left, get a cheap (unmanaged) gigabit Ethernet switch to expand the number of available ports.
That being said, setting up a personal media server is probably not the ideal solution for a “casual user”. You should expect a learning curve, requiring some time and readiness to learn. Both for the NAS unit in general, and Plex in particular.