The button has always been there for me (unless the video maker disabled it) just without a counter.
There is an extension that tries to crowdfund/estimate dislikes for youtube videos but who know how correct their data is [1]
Thinking again after your reply, It might have been there for me too and I just never noticed. Or it could be that my brain was malfunctioning when I posted this. Because now I think it really was there just didn't have the counter with it.
[1]:https://returnyoutubedislike.com/