Mac Mini Terminal opens Shell menu when clicked and freezes

Have you rebooted your Mac? If not, do so then try again. If you have, then see if the problem is present when you boot in safe mode, which disables 3rd party extensions and performs some system cleanup.

Start up your Mac in safe mode - Apple Support

Henry8 wrote:

Mac Mini Tahoe 26.5.1 click on an open Terminal window, it opens the Shell menu and freezes. Click on Safari stops the freeze - but still can't use Terminal.

I'm not sure what you mean it opens the shell menu.

Are you clicking on the "Shell" menu on the menubar of the Terminal app? If so, are you selecting an item on one of its menus with an arrow key on it indicating more options? If you don't actually go into the submenu & make a selection, but release it on one of those menu top level menu items with an arrow, then the Terminal may indeed freeze up. It is an intermittent & annoying bug I encountered several years ago. The bug does not occur if you make an actual selection on a submenu. Or use the shortcut keys to select an item.

You can provide Apple with product feedback here:

Feedback - macOS - Apple

Henry8 wrote:

Mac Mini Tahoe 26.5.1 click on an open Terminal window, it opens the Shell menu and freezes. Click on Safari stops the freeze - but still can't use Terminal.

Terminal>Settings> verify you are using the default shell...and compare your results.