By default, don't have any notifications show on your lock screen unless they're from close family or friends (or you're a SRE whose job it is to deal with problems at 2am, but that's another story). Any app that isn't specifically human-to-human-communication-based probably doesn't need to be sending you notifications at all, ever. Keep track of your weekly screen time notifications from your operating system, and be mindful of having that trend upward.
Set specific times in the day when you're going to look at random communications/email, and stick to those times -- if it helps, set a calendar time for that. The more you can get into that timed routine, the easier it is to reduce the total amount of time spent on distracting things and the more you'll be able to budget your time for deep work.
Social media, it can be really tempting to feel fomo with friends/coworkers/family/etc. You'll feel like you're missing out at first, but that feeling does get smaller and smaller over time. You don't need to cut it out 100%; but what you need to do is eg stop that quick 2-minute refresh of the Gram when it's 10:30am and you really should be more productive.
It isn't a magical self improvement routine, there isn't a promise of happiness, but eg reducing doomscrolling and reading shit comment responses and shit bird app threads and seeing shit clock app videos, it will give you a lot more mental energy.
Let’s break it down into common sense thoughts.
* Dopamine hits feel good.
* Anything that makes you feel good produces diminishing returns when repeated too frequently.
* For many people this can trigger addiction.
* If you get internally hostile to suggestions that you should try quitting such behavior: you’re an addict. Standard example: no one will get angry if it’s suggested that they stop eating cauliflower, but many will get angry if it’s suggested they stop consuming sugary products or drinking alcohol.
Therefore, an experiment where you quit the controversial item is harmless and will tell you more about yourself and just about anything else.