Preview icons for files are not displaying .... (recently updated to Mac OS Monterey 12.2.1)

On the Desktop, press CMD+J and make sure Show Icon Preview is checked. Navigate to where the files that are missing previews are located and then rinse and repeat to ensure the Show Icon Preview is turned on.

Try booting into Safe Mode then reboot back into Normal Mode. Booting into Safe Mode runs a bunch of maintenance scripts and also flushes the system caches and can resolve bizarre problems.

To boot into Safe Mode hold the Shift key while powering on. Let go to login then continue holding Shift after pressing Return. If the disk is encrypted you will have to login a second time. Keep holding that Shift key until you get to the desktop. Then give the systems 2-3 minutes to finish doing stuff behind the scenes. Then shutdown and restart normally.

See if after some time the icons start showing previews again.

I would guess there is some preference or configuration file damaged in your user profile on the Mac. Create a new user to test. Copy over some files to /Users/Shared and copy them to the test users Desktop and experiment a bit. If the problem goes away with the test user then the problem is within your user profile on this Mac.

I would then create a new user for myself, copy all the data over (since you have things in Cloud that shouldn't be anymore difficult than re-authenticating to the cloud system). Yes, this is a pain but if it works then the problem is solved. Once everything is perfect, you can remove the original user account as well as the test account and get on with life. You'll need to redo all your App settings, etc. But at least you will have a clean fresh start.

It sounds like PowerPoint is the main problem and if other files associated to other Apps are working... I saw JPG was working but PNG was not and PPTX definitely had issues. Try this first, select one of the problem files and press CMD+I to pull up the Get Info screen. Look at the Open With entry and make sure it's pointing to the correct application. PNG should be Preview. PPTX would be the correct PowerPoint. If you change say PNG to be Preview and the Change All button is clickable go ahead and click it. That will force Preview to the be default application for PNG file types. Repeat with PowerPoint files, etc.

The Microsoft for Mac Engineers have been pointing Mac SysAdmins to this tool to reset / repair Microsoft Office. One of the Microsoft engineers wrote it. https://office-reset.com

You could try that tool. Don't reset everything, just try resetting PowerPoint first. It will repair problems and reset the App to its default out of the box configuration. So you will need to redo any settings in PowerPoint.

Open Terminal and try this to reset the icon association database:

(copy the whole line and paste)

/System/Library/Frameworks/CoreServices.framework/Versions/A/Frameworks/LaunchServices.framework/Versions/A/Support/lsregister -kill -r -domain local -domain system -domain user

Try changing directories to the location first:

cd /System/Library/Frameworks/CoreServices.framework/Versions/A/Frameworks/LaunchServices.framework/Versions/A/Support/

Then run the command from within that folder:

./lsregister -kill -r -domain local -domain system -domain user

Safe Mode on an Apple Silicon Mac (M1, M1 Pro / Max):

1. Shutdown completely
2. Press and hold power button for about 20-30 seconds until the Mac boots to a Recovery Mode
3. Hold Shift and click on the Macintosh HD drive and there should be a Safe Mode option below the icon, click that to boot into Safe Mode.

*Added for those with Apple Silicon Mac's the Intel Mac's you hold Shift at power on.

Try rebooting the Mac. I don't know if those settings will kick in until Finder is relaunched or a reboot occurs.

Can you provide a screenshot as an example? Is it just picture file types (JPG / PNG) and PowerPoint? Or is it everything?

What version of PowerPoint do you have? PowerPoint menu -> About PowerPoint.

Apple switched from bash to zsh due to software licensing. The bash shell adopted a more rigid open source license so Apple switched to zsh which has a different license and zsh is more advanced anyway. But none of this actually matters in your case. Bash is still there and it still works. The message is merely informing you about it.

You can ignore that message, the bash shell will work just fine.

Please try the steps again.