Is there a way to remove the "billible" option on vendor bills so I can make old vendors inactive?

I know a way for you to untick the Billable box, Oldhickory. Let me walk you through the details.

In QuickBooks Online (QBO), you can untick the Billable check box within the Bills transaction. Afterward, you can save them. If you already have existing transactions, you can edit these transactions by following these steps:

1. Go to the Expenses menu in your left navigation panel, then choose Bills.
2. Click the Unpaid tab.
3. Find the transaction you'd like to edit.
4. Double-click the said transaction to modify.
5. From the Category details dropdown or Item details dropdown, you can untick the checkbox under the Billable column.
6. Click Save and Close.

Afterward, you can utilize this material to inactive your customer: Add a vendor in QuickBooks Online.

If you have duplicate accounts, customers, or vendors, check this article on how to merge them: Merge duplicate accounts, customers, and vendors in QuickBooks Online. 

Let me know if you have other concerns or have follow-up questions about it. I'll be here to help.