You do not need to do all of this. Begin with the part that feels kindest.
Reduce the number of doors
Attention leaks through open choices. Close the extra tabs, move the phone out of view, and decide what finished means for the next twenty minutes.
Use sound as a boundary
A consistent low soundscape can mark the beginning of focused time. Pick one without lyrics or dramatic changes, and use it often enough that it becomes familiar.
Stop before depletion
Take a short break while you still have some attention left. Sustainable focus feels less heroic and more repeatable.