Videos won't import, previously imported videos won't play

Running Lightroom CC Classic 8.1 release (build 1200465) - latest

On Windows 10, European 'N' addition -> meaning it excludes certain bundled multimedia functionality, including media players and related components. So I DO NOT have Window Media Player. I'm using VLC for all my media playback.

Fairly new clean OS install. Using a previously created Lightroom catalog. Previously import .mp4 videos (that used to work before the fresh system install) aren't working anymore. If I try and open them I see "there was a problem working with the video"

Furthermore, I can't even import new .mp4 video files. I get "An unknown error occurred while reading the video file"

I tried purging video cache, tried creating a new catalog, tried turning off 'use graphic processor'. Nothing helps.

I have a hunch this issue is because I'm using VLC?

Found something related: Solving Lightroom’s “There is a problem with the video file” Error | Lightroom Fanatic -> see very last post in the thread by 'Cass', specifically:

"I also noted that the video files I had problems with (MOV and AVI files) were associated with VLC media player. So, I did the following: –

1. Rebooted machine
2. Set default program for MOV to Quicktime
3. Set default program for AVI to Windows Media Player, which was run first time
4. Launched LR, initially clicked off ‘Limit video cache size’, clicked back on, hit purge cache
5. Cache was purged within 5 seconds
6. Attempted to import all video files that previously had not imported
7. All previewed and were imported completely fine"

Installing Windows Media Player is NOT an option for me. Is this a Lightroom bug? Any suggested fix?