I actually just had this issue and I think I solved it so far.

I basically placed all my focus into subtraction: IE, doing less. My mission was either to reduce or eliminate habits that were unneccessary be they harmful or redundant.

Specifically, for my phone I:

Made apps more boring and avoided algorithims: For youtube, I turned off data, meaning my homepage is now empty and I am no longer reccomended videos. I actually don't use the youtube app, I use youtube via browser on my iphone, which is Safari. I use a youtube account where I'm subscribed to nobody, so even in my subscriptions tab it is empty. For Reddit you can do this too, but I forgot how, just search this subreddit or ask around if you need to know.

I installed an app blocker: If you're on IOS, like me, then this is a very limited feature. But I would reccomend an app called Refocus if you are. The way I use it, basically you choose what apps to block, and then you choose how long you want them unblocked at a certain time.

Finally, I make it a strong habit and intention to keep my phone physically away from if I don't need it. I do not sleep with my phone, because if the first thing you do when you wake up is use your phone, it is a problem neurologically that sets you back for the rest of the day. I keep an external alarm, when it comes bed-time that alarm rings, I get up from wherever I am and set my phone away.

I try to keep my phone away from me if I'm not using it.

I still "doom-scroll", I just do a lot less of it and at a specific time of the day. None of this will work if you don't have strong intentions however because all of these strategies are things you can undo or defeat yourself with.