Refined Message Selection Excluding Folders

I need a feature where the 'Select All' function chooses only the messages that are not within any folders. Currently, it selects everything, including the contents of folders, which isn't what I want. Ideally, only the messages in the main inbox or outside of any folders should be selected. A potential workaround might be to use the star function to differentiate messages, preventing starred items from being selected, but I'm open to suggestions for the simplest solution.