Hi @Bowen Zheng ,
did you try to clear your browser cache? That's the first thing I'm doing when sth like this is happening.
Atlassian frequently releases security updates for Confluence. It's possible the attachment download security feature you're experiencing is from a more recent, non-public update focused on improving security measures. Could be that an update prevents some file types from opening directly in the browser. Can you download the file?
And third: Have you tried a different browser?
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