YouTube also added a shorts timer that does a more in-app version of this that you can set to 0 minutes to have it always on. It's under "time management" in the app settings. Can't do it on the website from what I'm aware.
I use YouTube in browser, partially because that already makes it worse… but still doesn’t stop the doom scrolling :)
Only thing that worked for me long term. My problem is mostly with shorts, so I didn’t want to have a global timer for the whole app.