Mac client, can't download .pptx file from zulip message

[sanfords]

Describe the bug

Unable to download file attachments from the Mac native client.

1. Attach a powerpoint ppxt file to a zulip message.
2. View that message with the native Mac client.
3. Click the link in the message to download the ppxt file.
4. Nothing happens, it just beeps. This is in the debug console:

'Granted permissions request for notifications from null'

I'm seeing the "downloadFileCompleted" event in the debugger bug couldn't race back farther.

For the download to have worked.

Desktop (please complete the following information):

• Operating System: macOS Big Sur 11.3

• Zulip Desktop Version: 5.7.0

Additional context

Downloads work if I bring up the conversation in a web browser.

This does not appear to be a problem with .ppxt specifically.

[bendyarm]

~~Also having this problem on Zulip v5.9.3 on macOS Catalina 10.15.7.~~ That was due to user error. I see now that it downloaded.
Duplicate file numbering is nonstandard, which misled me when I glanced at the downloads.