How stop boxes when I click Mac mini screen?

brutus inquisitor wrote:

When I click on Mac mini screen I get a large (green) box outline.

How do I get rid of this useless, distracting rubbish?

Mac mini, macOS 26.0

I might suspect some Accessibility feature got turned on...(?)

>System Settings>Accessibility>

you posted in macOS Sequoia, your byline says macOS 26(?) so which is it exactly.

There are a few screen artifacts that have appeared in the new OS Tahoe, did you try shutting down the Mac and then restarting the Mac to sort anomalies? >Shut Down

Do you have other things on your Desktop?

Are you saying in Mission Control?

A screen shot is worth a thousands words (Shift Command 3)

Do you have Full Keyboard Access enabled, by any chance (System Settings > Accessibility > Keyboard, top setting)? If so, turn it off.