For the distractions, one thing that helps me is removing easy access to them.

Just like having junk food in the house means that I will tend to eat junk food (but I won't go buy junk food on impulse)...

* Remove the time-wasting capabilities from your devices (e.g., uninstall apps, set up uBlock Origin blocking rules for anything TikTok-like, block HN for a week).

* Make dedicated distraction devices hard to access (e.g., unplug gaming rig/console and store it away for a week/month, same with the living room TV/screen, sell that handheld gaming device).

Also, once you get some momentum on a better activity, it's easier to stay doing it. You might have to lock away all your distractions for a few days before you can get immersed in that coding side project (or writing that novella, or that new workout routine). But then it can become a go-to activity that you do automatically, and maybe even think about at other times, rather than defaulting to doomscrolling.

(I don't claim to always do this myself, but when I do, it works.)