Here's another update: I was looking at the WD drives that markjames had suggested, but alas, they were all $100+ even on ebay. I checked amazon for something similar and found this:
https://smile.amazon.com/gp/product/B008NO9RRM . I figured for $40 I should check it out as something for my mom.
I hooked it up to my home office TV, went to the correct HDMI port, turned it on (it comes with its own small remote), and it started up with this screen ...
I chose "movie" (the choices are "explorer," "music," "movie," "photo," and "settings") and it went to this screen:
I had connected my external Seagate hard drive to it so I chose "USB device," and it went to it. I clicked on it (it was just listed as "USB device (f: )" and got this screen ...
I had created a folder and added 1 .mp4 file to it so I could test the Micca device. When I clicked on the mp4 folder, I got this:
And so I clicked on the 1 movie I'd added, and after about 2-3 seconds' buffer time, it started right up. Here it is about 11 minutes in:
So I am going to pack everything up again and send it to my mom as part of her birthday present. She is about to turn 85 and gets VERY frustrated with technology, so I wanted to make sure it was very, very simple before I sent it to her! I'll have my sister (who lives near our mom) set it up for her, but then she'll just have to choose the HDMI port, choose "movie," choose "USB device," then choose a movie. I HOPE it goes well!
One quick note, I had originally hooked up a 4tb drive to it and it would go to the device but never list the files. I thought it wasn't going to work, but then I realized that the description says it will work with devices up to 2tb. Once I switched to my 1tb Seagate drive, it worked as expected.
I am thinking about getting one of these for when I travel -- it's a tiny device with a small (Roku-sized) remote so it and a USB external drive won't take up much room. (I THINK I am supposed to be able to connect to my Plex from anywhere, but I usually shut down my home network when I'm gone.)
Anyway, hope this is helpful.