Your screenshot can’t be saved - Unable to capture window image

have you tried "shift-command-3"? that shortcut combination should give you a full screen screenshot.

sorry, I misunderstood what you were asking. I tried what you are describing, and with "shift- command-4" and then "spacebar", it does select just a certain window. and upon pressing "return", it does save to my desktop. so it appears to be working here. I think since yours isn't working as desired, I would try and Start up your Mac in safe mode. and if it works in safe mode, I would leave the Mac in safe mode for roughly 5 minutes and then restart normally. sometimes a safe boot followed my a normal boot will solve some anomalies.

and if it does work in safe mode, but not after a restart, I need to ask, do you have any apps that claim to "speed up" or "clean up" or otherwise "optimize" your Mac? and / or do you have any antivirus apps installed?

if none of those types of apps are on your Mac, i'm thinking you should download and run the free version of EtreCheck so we can see if you have some software installed that is causing your issue. make sure you give "full disk access" to etrecheck. Learn how to use it by reading Using EtreCheck. if you need help interpreting the report, you can see how to post the report here by reading How to use the Add Text Feature When Posting Large Amounts of Text, i.e. an Etrecheck Report. and it automatically obscures sensitive things (like serial numbers) so you don't have to worry about sharing the report here.

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