I find productivity is a false metric to measure yourself against. The most productive person is the person who writes the most code / features, but usually the most important people don't write code, they help others, whether that's understanding problems or giving direction.

I still agree with the title, I give my attention to as much as I can handle, and no more. I have (restricted) notifications turned on, I try have interesting things around me, I tackle as many problems as reasonable at the same time, but slowly because I find the best solutions are where I've had a while to think about while in the shower for example, and how they interact with other problems.

PS: if you're trying to learn something, disregard everything I said, focus is so important when learning