I disable notifications on stuff like this. I don't want to get interrupted by random notifications every few minutes/seconds. The vast majority of slack messages are not worth being interrupted for. The very few messages that are an exception to this are a small sacrifice. I got in the habit of scanning the slack UI every once in a while to see if anything needs my attention. So, I pull notifications rather than getting them pushed to me. I check less often when I'm busy.

I find that if you don't respond in real time people around you adapt to that. If you always respond instantly, it lowers the barrier for them to bother you more. So, you'll be dealing with them constantly. If you simply delay your response, they'll adapt and be less likely to interrupt you.