Problem
The YouTube user ProsafiaGaming is a popular channel on YouTube who is notorious for spoiling the final boss in New games within the thumbnail

Solution
For the user to simply alter his thumbnail style to not spoil the final boss such as blurring it out he is not required to stop his production just don't spoil the fun for other people

Personal story
Once I was really enjoying mario oddesy and I was close to beating it until his video was in my recommend and ruined the boss for me and I know many people who have had similar experiences