I write my to-do list for the day on the previous day just before I go home. Then, as soon as I come in, I have an unambiguous list of things to do, one by one

I write my to-do list for the day on the previous day just before I go home. Then, as soon as I come in, I have an unambiguous list of things to do, one by one, and I commit to not deviating from the list, unless the world is on fire. That makes it easier for me to ignore Slack, but even if not, I'll see messages come in, and unless they sound like fire, I go back to my list. Not sure if helps, but I found it quite helpful.