As suzumer also commented, the extension Unhook has also been very helpful to me in curbing the amount of time I spend watching YouTube. I have it set to block the front page suggestions, sidebar suggestions, after video cards, etc. Everything except a particular video I'm searching for. And of course I always view youtube logged out.
The first thing I did to try to curb my...addiction to YouTube was to consume the videos instead through RSS feeds. I wrote a script omnavi (https://sr.ht/~smlavine/omnavi) to help out with that. I would never watch videos on YouTube itself; I would click links that I got through RSS to channels I was subscribed to, and view the videos locally with mpv + youtube-dl.
Honestly it's sad to look back at how many hours of my day I wasted watching YouTube videos. They're the sort of sort-of educational videos that make me feel like I'm spending my time valuably, but at the end of an all-night session, I really wouldn't have been able to tell you any of what I had watched for the past six hours.