It's delusional to think that most software projects can be planned in advance beyond "there will be a beginning, a middle, and an end". People do it, but their efforts are in my experience generally ignored once implementation get underway.
Planning in software isn’t about following the plan but mapping a viable route to avoid predictable issues. You’re always going to know more about a project as you build it and you should keep updating that plan.
That’s true at the project level. But surely when you sit down to actually work for a couple hours you think about what you are going to do, and then mostly do that.
In my experience it’s more fractal. Any subgoal, however small, may run into its own planning/thinking and then doing sequence, or even have you reconsider the higher-level plan. Of course, it somewhat depends on how run-of-the-mill the overall task is.
