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Turn on the view bar, sort by flagged. All of your flagged projects will be shown before all of your unflagged projects.

If you want to see all of your projects arranged by due date, turn on the view bar, group (or sort) by due.

The general notion behind OmniFocus is that you execute from context mode, choosing from the actions available to you in the context(s) you occupy. That way you don't waste time scanning actions you can't do at the moment. Naturally, if you want to focus on a specific project and work it until done, you can do so, but that would be done in project mode (aka planning mode).