Applications will not open in Finder
Applications in Finder are not highlighted and won't open
MacBook Pro 13″, macOS 11.1
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If the application has a do not enter icon on top and you are using Big Sur, or Catalina, it has not been updated to 64 bit for compatibility with Apple's newer operating systems on your system, and you will need to research if updates are available.
If the MacBook Pro is a new M1 chip according to Apple menu -> About This Mac, some older Intel only applications will not work.
Backup your data to another drive before going to the next step.
If no application will open in your Applications folder in your hard drive, and their icons look normal, your launch services program may be corrupted. This can happen if you install any system optimization tool from Mackeeper to Advanced Mac Cleaner, to anything else by Zeobit or Macpaw. You will need to take it to a service center or connect another Mac to it, that has tools to locate the preference files and executable documents for these cleaners.
https://support.apple.com/en-is/guide/mac-help/mchlp1443/mac
explains how to link another Mac to it.
And Devon Technologies, EasyFind is a great utility for locating files deep in the bowels of the Mac that is linked in target mode. When in doubt, don't touch.
https://download.devontechnologies.com/download/freeware/easyfind/5.0.1/EasyFind.app.zip