Normally, when you save a file that has the same name and size as another one, the Mac operating system will always ask you if you'd like to replace the file that already exists. If you used 'Replace', the file labeled with the same name as your new file is overwritten. That is what we call an overwritten file/replaced file.
The replaced file will still store on your Mac internal hard drive until a new file is written in its place. But you can't find it from any folder or location on your Mac using Spotlight because once the files are replaced by new files, the operating system will automatically remove them to free up space. You can consider your PPT file was deleted from your Mac drive temporarily. To recover it, you can use Time Machine backup, iCloud backup, and data recovery software.
iBoysoft Data Recovery for Mac is a professional data recovery software to recover replaced files on Mac. This powerful data recovery tool is compatible with Intel Macs and Apple Silicon Macs with M1 and M2 chips and also works on macOS 13/12/11/10.15/10.14/10.13/10.12 and OS X 10.11, which is also able to recover emptied Mac Trash.
To recover the replaced files from Mac using iBoysoft Data Recovery for Mac. You only need to download and launch it. Then use the Search for Lost Data function to start scanning all lost files on your Mac. Once the scanning process is finished, you can filter these recoverable files by different file formats so that you can quickly pick up the replaced PPT file.
You can preview the PPT file you find to ensure it is the one you need, select it, and click "Recover" to retrieve it from the Mac disk. Rember to not store the recovered PPT file in its original place to avoid data loss.