Your input is important, and I appreciate you taking the time to reach out here in the Community space, @JulieT711. I'm here to offer a solution to address the auto-selection of inactive categories when entering a check in QuickBooks Online (QBO).

Before, you'll want to check and verify the Vendor's Profile to see if there's a default expense category associated with your vendors. These are the steps:

1. Access your QuickBooks Online company.
2. On the left navigational bar, click the Expenses tab and select Vendors.
3. Click on a vendor and then select Edit.
4. Scroll down to the Accounting field and ensure there's no expense category.
5. Once done, click the Save button.

You can check the image below for visual reference.

Once verified, head over to the Account and settings, and then make sure to disable Pre-fill with previously entered content. Here's how:

1. Access your QuickBooks Online company.
2. On the top right corner, click the Gear icon and select Account and settings.
3. Go to the Advance tab and then head over to the Automation section.
4. Click the Pencil icon and toggle the Slider icon beside Pre-fill previously entered content.
5. Once done, click Save and then Done.

See the photo below for reference.

Additionally, you can check out this article to help you managing vendor bills and payments in QBO: Enter and manage bills and bill payments in QuickBooks Online.

I'm always ready to respond and lend assistance in addressing your QuickBooks-related inquiries. You can communicate with me in the comment section so we can team up again and resolve obstacles you encounter in the program. Stay safe.