Oh, and I also have a wired 1 GB ethernet connection, so bandwidth should not be an issue.
After reading the discussion, I think I am okay with hardware. The ReadyNAS has 4 3 TB hard drives, so if I use it for just storage, I should be fine. But I would still need to know how to set up Plex Media Server for Windows 10 in order to access all the movie files on the ReadyNAS. Of course, there will be plenty of room for both the 4K and 1080P versions of the movies.
Thank you for all your help, oh Ninja Master! LOL
Actually, my original question about the subtitles has not been answered yet. How do I get those to show up on the Samsung TV?
I did some digging and got the following input:
For Plex on Roku to be able to display subtitles, the Roku itself has to be configured to allow ācaptionsā.
To be safe⦠also double-check the settings in the Plex app on your Roku.
- In the Plex for Roku app settings:
Settings > Subtitles > Roku Captions Mode > On - In the Roku OS system settings:
Settings > Accessibility > Captions mode > On always
Thank you, Plex Ninja. I am now happily seeing subtitles for Plex movies on my TV screen. Great discussion! 
For the record:
Parasite doesnāt need Forced Subtitles.
Forced Subs are used when there is some Foreign Dialog in an otherwise English/Other dominated item. Forced subs will contain those Foreign lines.
Parasite has Korean Audio.
What you need are the full subs - your settings tell Plex to turn on some subs with Foreign Audio - and they should not be Forced. Technically.
This does require you actually tag your files with the proper language:
movie audio - Korean
Subtitle - English
I didnāt create the mkv file, JuiceWSA. However, it already is tagged as Korean audio.
Not sure what you are saying about the forced subs, but the subtitles are working fine now. Iām kinda of the mind āif it aināt broke, donāt fix it.ā 
Itās confusting and Plex doesnāt clear it up any, but:
Midway (1976) - will use Forced Subs so you can see what the Japanese guys are saying in Japanese - since you donāt speak Japanese.
Parasite (2019) doesnāt use Forced Subs 'cause there aināt anything BUT Korean and Plex knows you need the full track - or youāll have to use the Vulcan Mind Meld - on your TV.
You may not have to fix it right now, but there will come a time when knowing the difference will be of some value.
Thank you for your comments, JuiceWSA. I will keep that in mind.
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