I've checked and verified that we have an investigation about the error 1001 when downloading transactions in QuickBooks Desktop for Mac. Our Engineering Team is now working to resolve this promptly.
With this, I suggest contacting our Customer Care Team. This way, they can add your account information to the list of affected users and attach your case to the investigation. Any progress will be communicated via email.
Here's how to contact:
Go to the Help menu, then choose QuickBooks Desktop Help.
In the meantime, our recommended workaround provided by the engineers is to download the bank transactions using Web Connect, if your bank offers this service.
First, you'll need to download the transactions from your banks' website and import it to QBDT. I'd suggest contacting your Financial Institutions (FI) if you're not sure how to download the QuickBooks Web Connect file (.qbo) from the website.
Once done, let's go to the Banking tab to import the data. Then choose Downloaded transactions, and hit Import File. For detailed instructions, check out this article: Set up and use Online Banking (Mac).
Please browse through these articles to learn more about how to resolve issues when using Online Banking and other related topics.