Hi @LUFC
Welcome to Q&A forum.
If you are using mail client, it is recommended to try the online mailbox and download these files for a test.
Please right-click on these .pptx file and select Properties from the menu, and take a screenshot of General tab.
I suggest you check whether there is Unblock on the General tab.
If yes, you could tick this box.
Please also check the the application of "Open With".
If it is not PowerPoint, you need to click "Change" to select correct application to open.
Besides, if you have any anti-virus software, please turn it off temporarily.
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