But it's critical to avoid waiting too long to make decisions. Because that means the decision was to make no decision, and that has only a random chance to be the right one for you.
Planning is a big part of how you have the information you need to know when to make a decision and when to defer it.
Plenty of work be organized to fit into ~two-week, focused sprints, and can be done efficiently that way. Use your planning to figure out what should and should not be tackled that way.
There's also work where it makes no sense at all to do while looking ahead at most only two weeks.
For instance, if you have a good experienced architect, a small amount of time spent on a high-level arcitecture will pay you back on even a slightly successful project. Not to mention it will increase your agility. E.g., don't design a sophisticated privilege mechanism until you know you need it. But if there's a reasonable chance a privilege mechanism will be important in the future, know where one would fit in in a way that wouldn't require a substantial rewrite. Now you'll be able to slot in a simple privilege mechanism, if/when you need one, and later replace/evolve that with a sophisticated one, if needed, all quickly and without substantial rewrites.