I completely agree that open offices designs are completely terrible and make work very stressful. I don't see agile and slack as equivalents though as how they get implemented completely dictates how this plays out. My current work is agile and we use slack and I have 0 problems with being interrupted. We also don't have the issue with open offices as well, given that we are 100% remote.

Personally I think the fully remote fixes half the problems in this area as it makes meetings harder and emphasizes communications like slack as being real channels (with processes and conventions), vs. a side channel that people feel easier to bug you personally on.