YouTube has recently hidden the number of dislikes for YouTube videos. In a blog post from November, YouTube announced that this was done to "help better protect our creators from harassment, and reduce dislike attacks". The dislike button hasn't disappeared, but the dislike counts were made private, so that only video creators could see them.
If you install this Chrome extension, you can bring back the number of dislikes next to the "dislike" button. Unfortunately, YouTube removed the ability to obtain the number of dislikes from the API, so the extension uses archived data and the number of dislikes from the extension's users. The extension has "200+ million videos likes/dislikes data stored before December 13th, 2021". This means that the number of dislikes displayed by the extension may be inaccurate, but it's still better than no information.