I found this video hugely helpful, I think it explains very well what kinds of activities need to replace it. I've found it somewhat helpful to get some physical puzzle books (e.g. sudoku etc) to keep around for this kind of thing, and when I get into that totally drained state where even scrolling isn't working any more I often do just step away from the computer and pick up my kindle or a puzzle book now instead.
I struggle with too much scrolling on and off. I actually think I probably have internet addiction, I meet all the criteria for it esp when I'm at my worst with it. It takes up so much time, it's actually awful how much time I spend staring at a screen.
It got a lot better when I first went on ADHD medication but I have slipped into it a bit again. Although I still think it is much better than I used to be, I would like to get it down further. For me the specific site doesn't really matter - I've been through phases where MN is part of it, then when it's not, sometimes it's reddit, sometimes instagram/FB, sometimes little hobby things.
It does help to try and notice what kind of thing you're thinking/feeling when you go on it - is it just automatic, (in which case there are apps you can get which introduce a delay which can help interrupt that cycle) is it that you're looking for something in particular, avoiding anything in particular? I think for me, I often tend to look to the internet for social connection, so I made a conscious decision to withdraw from some of the smaller online groups/communities that I was a part of and just stay in one that felt like I had real friends in it, and make a conscious effort to connect more with IRL friends by saying yes to things that I'd usually swerve, and sending people individual messages when I saw something that made me think of them etc. This is helpful because it means that I am doing less cycling through 6-8 online groups where I don't really know anyone in them but I feel as though I do, and using that time to connect with people that I have an actual likelihood of maintaining an offline relationship with.
I also think I can use it to sort of withdraw from RL sometimes if I'm a bit overstimulated or getting like my energy is drained. Because being online is anonymous I don't feel like I mask as much or perhaps because I can just passively consume without putting much in. But I do tend to get drawn into writing replies and I find I can do this even when IRL I feel too exhausted to move or speak. I also think that I tend to try to escape int my phone/computer in order to avoid feelings of anxiety IRL. Making more effort to understand my sensory needs and unmasking a bit and generally trying to be clearer with myself about my energy levels helps a bit with this in that I end up in this state less often. But it's a self-fulfilling cycle because if I spend too much time online I neglect responsibilities and then the responsibilities become more draining and then I'm too tired to do much except go online. I am also then more used to the energy expenditure of being online rather than doing things IRL.
Then lastly I think one thing I tend to get from being online is validation/feeling competent. It's easy to feel competent and helpful online if you are articulate and good at googling things, and because I've struggled IRL to find roles where I feel competent and valued (probably again because of my ADHD) I suppose I have leant on this a lot and then again it creates a bit of a self-perpetuating problem where the level of competence I feel when I respond to a post online and someone says it's helpful to them just does not translate to being good at anything IRL. I might be intelligent (they said I was at school) but that doesn't mean anything because I don't have qualifications or much RL work experience. However since I noticed this is one of my motivations, I've started to put a lot more focus into things which do build competence that I can use IRL because I know that I can be helpful and supportive to people and I do have knowledge which can be useful IRL and I actually just need to put in the effort to gain either concrete skills (like I've been working on my second language proficiency) or qualifications or experience using my knowledge etc IRL.