Here are some things to try if you’re having trouble opening or displaying inserted files in OneNote for Mac:

1. Close and re-open OneNote.

2. Restart your Mac.

3. Make sure the file type is supported by OneNote.

4. Try opening the file in another program or view it in Finder or Explorer.

5. Ensure you are signed into OneNote with the same account that you used to insert the file.

6. Update OneNote with the latest version.

7. Contact Microsoft Support.