You still have the option to manually tick the Save credit card for future use when adding a customer's credit card for your Sales Receipts and Payments in QuickBooks Online (QBO), Frank.

However, since it’s auto-saving on your end and you’re unable to manually tick the option to save the credit card for future use, I recommend clearing your browser’s cache to rule out the possibility of outdated or cached data causing this behavior. Alternatively, you can also use other supported browsers.

Here's a sample screenshot for reference:

If you have other questions, feel free to comment below.