I appreciate you for coming back to the thread and clarifying your concern, berwick12. I've got steps to ensure you can add a test company under your existing company and change the bank feed efficiently.

Beforehand, please know that QBDT 2020 is already discontinued. With this, you won't have access to live technical support if you run into problems or any of the other Intuit services that can be integrated with the program. Also, discontinued versions won't receive the latest critical security patches and updates and that's the reason you're unable to fix any errors and issues that you encountered on the said version.

Then, you can go to the No Company Open window to start doing or creating a test company underneath your current company. 

Here's how:

1. Open QuickBooks. You'll see the No Company Open window. 
2. Click Get Started. 
3. On the next window that appears, click Start Setup.
4. Log in to your Intuit account if you have one. If you do not have one, click "Create an account" and enter your information to make one.
5. Once done, log in to your Intuit account and create your company file. First, specify the name and location for saving your company file. Click OK, then enter a password on the Password Required window.
6.  Enter information about your company and click Next.
7. Next, you'll see the "Choose your industry and chart of accounts" window and enter the necessary information.
8. You'll see the location on your new company file in the final window. Click OK.

On the other hand, you can follow the steps below so you can change the bank feed or switch between banking modes on your end. Before doing so, make sure to update QuickBooks to the latest release and you're in single-user mode. 

1. Go to Edit, and then select Preferences.
2. Select Checking then go to the Company Preferences.
3. In the Bank Feeds section, select either
1. Advanced Mode: This uses the Transactions List window to add or match transactions. You can quickly update transactions for future matches or create rules to automatically recognize and match transactions to your books.
2. Express Mode: This uses the Transactions List window to add or match transactions. Renaming rules are created automatically.
3. Classic Mode: This uses the account register to add or match transactions. Aliases match names exactly and you control when you want to create aliases.
4. Select OK.

In addition, you can refer to this article to see the detailed troubleshooting steps on how to resolve the OL-222 error you encountered: Fix error OL-222 in QuickBooks for Mac.

In case you need to see what’s included in the QuickBooks Mac Plus 2023 release and how you can use them to benefit your business, you can read this article: What's new in QuickBooks Mac Plus 2023.

Don't hesitate to tag my name in the comment section if you have follow-up questions about managing company files and any banking-related concerns. I'm always here for you, berwick12. Keep safe always.