Apple - Why is is not possible mark text in my Terminal window anymore?

Sometimes things go wonky in the preferences files and you need to delete them to get things working properly again. Once you restart the app, it will rebuild it's preferences.

Try this:

Quit Terminal completely and then delete this file: (your home folder)/Library/Preferences/com.apple.Terminal.plist

Hopefully that works for you! If you can't see your library folder, follow this quick guide.

It's possible that mouse events are captured by the program running in the terminal. For that to happen:

1) The program must be written to support mouse (vim and tmux are both examples of such programs), and

2) Terminal must be in Mouse Reporting mode. This mode is enabled by default.

If you disable Mouse Reporting (View/Allow Mouse Reporting, ⌘R), mouse events will not be captured regardless of whether the application supports mouse or not, and you will be able to select and copy text.

I had this problem and solved it just by quitting the terminal completely and opening it again.