I don't know what's the cause of not able to preview or download email attachment. Google Drive notified me to delete some files because 15 Gb of free storage is already full, so I deleted some files to free up space. I also upgraded my Android phone into Android 12. So I don't know what's the cause of not able to preview or download email attachment. But thanks to Microsoft Outlook, it solved my problem. Bye for now Gmail, I'd rather use Microsoft Outlook for now.