What helped me a lot was getting up very early.

I wake up around 04:30/05:00 (without alarm), make a coffee and work till 8 or 9. So i already worked a lot without getting notifications or emails from co-workers, they are still sleeping.

Around 9 i have a shower and make a little break. Around 10 i work again till 1pm and the rest of the day i'm still online for my co-workers, but not really working anymore. After 1pm i mostly work on my own projects or do groceries and so on.

What really helpmed me are Qbserve (https://qotoqot.com/qbserve/) to track my productivity and Flow (https://flowapp.info), a Pomodoro timer. I can block social media and other stuff with Flow to don't get distracted in the morning. I don't open social media (also HN) before 1pm.