Hey there, @LJK1970.
The option to show the $$$ amount on an invoice is unavailable in QuickBooks Online. For now, you'll need to enter an actual number to record the late fee.
In addition, how late fees are showing as line items depends on the type (amount or percentage) that you've set in Account and settings.
For additional reference about applying late fees, check out this article: Apply late fees to overdue invoices automatically in QBO.
Moreover, you can personalize and add specific info to your sales forms in QuickBooks. This way, you get to decide what info your customers see and only add the info that matters most to your business.
If you have further questions or queries about changing the text showing in the late fee amount on invoices, add them to the thread. I'm always here to provide more clarification.