I don't get it. I've purged and reinstalled VLC. If I run VLC and open media from there, works fine.

But if I double click from pcmanfm, it doesn't do anything. If I right click and select VLC it doesn't work. If I right click and select open with vlc it doesn't work.

As I test I installed mpv and that works fine from pcmanfm. VLC works fine on my other two computers from pcmanfm.

Also, probably unrelated, but if I try to edit the icon the window size is enormous, I can never get to the bottom right so I can't save any changes. https://i.imgur.com/uxwUQy1.jpg

now that you mention it, I've experienced something like this, double click a movie in pcmanfm with VLC being set to default movie player and nothing, I've never paid much attention to it,just taking in the effects, and wonder why that happened, then I'll just right click and select mpv player. I do not think it was for every movie that this took place, only on certain movies, so I wrote it off as the movie must be "funny".

that is in Manjaro, as I am in Slackware current now, and just tried it, and it fires up a movie right click select VLC and double clicking on it works too. ver 3.0.3 Vetinari. it maybe the movie data, does it do this with every sticking movie you try it with?

then adding the factor of VLC Works and re-thinking again. it cannot be VLC, it should/has to be the mechanism between VLC and PCMANFM if VLC is playing them using it to open them. therefore VLC is working, it is the mechanism that causes the firing off of the app to start.

I'd start by looking at the MIME Editor, you could look in that to make sure the movie type is associated with VLC for starters.