How change the thumbnail in windows 11

In windows 10 I used to change the thumbnail for a mkv file attaching an image and naming it “cover”, but now on windows 11 it doesn’t work anymore and all the videos created previously on windows 10 now have lost their selected thumbnail and have a random frame (usually the first of the video or one of the firsts).
Is there still a way to change the cover with mkvtoolnix? Is there something that I am missing?

Welcome!

I actually don’t know as I have no idea how Windows in general & Windows explorer in particular generates thumbnails, neither in general nor for Matroska files in particular.

Thank you for the reply, I solved it with another program, Icaros, that fixes this thumbnail problem on windows