One thing at a time sounds slow. It’s actually how anything gets finished.

Doing several things at once feels productive because there is constant motion, but almost nothing crosses the line, and unfinished work keeps charging you rent in attention. One at a time looks slower per minute and is the only method with a reliable record of producing finished things. The value sits in completion rather than in effort.

Pick the most annoying unfinished item you are carrying and do only that for forty minutes today. No tabs, no parallel jobs. Finish it or get it to a clean stopping point, then start the next. Two finished things beat six half-done ones by a mile.