Saw this video. And it changes depending on if I view the thumbnail in my browser or in private mode/logged out of YT. Went back on their channel page logged in and it remains saying “You Are Not Right Wing” so it’s not specific to their channel page showing a different thumbnail.
YouTube also will not stop trying to show me right-wing “downfall of Canada” videos. Maybe YouTube thinks I’m right-wing.
You can set different thumbnails for different platforms I think