I’ve had problems too getting Plex to work but now it seems to start…
Running a freshly updated Windows 10 Pro N version 20H2 build 19042.330 and mfplat.dll file version 6.2.19041.64 product version 10.0.19041.64 is located in C:\Windows\System32 but this gave me a missing mfplat.dll error.
When I copied this file to the Plex installation directory I got another error, 0xc00007b, indicating the application could not start correctly. This version worked: https://www.timekills.org/public/mfplat.zip, this is is file and product version 10.0.15063.332
So an older version is required, I think this is to blame on the Plex developers that use an outdated/deprecated library, not Microsoft’s fault…
Those having issues installing Media Pack, there is also another way to get it via the OS.
Media Feature Pack for Windows 10 N (May 2020)
Microsoft Optional Features
The Media Feature Pack for N versions of Windows 10 is available for download as an Optional Feature. To install the Media Feature Pack, navigate to Settings > Apps > Apps and Features > Optional Features > Add a Feature and find the Media Feature Pack in the list of available Optional Features. Note, you will not be prompted to restart your computer, but you must restart in order to successfully complete installation of the Media Feature Pack.
Exactly the same problem and thanks @mfzarecky_gmail.com for the solution, worked a treat.
If you upgraded Windows and you run into this problem, just look for the windows.old directory, go to syswow64, copy the mfplat.dll file from there and paste it into the c:\windows\syswow64 directory.
The best way to do this and make sure you get the correct one is via “Add optional Features”
1 - Right Click the Windows Logo
2 - Choose Apps and Features
3 - Click “Optional Features”
4 - Press the “+” sign where it says “Add a feature”
5 - Search for “media pack”