I turned on Make expenses and items billable, although I don't understand how that applies. These are not expenses, they are time charges coming from QuickBooks Time. It also did not change anything - still can't add them to existing invoices.

All of the time charges are definitely marked as billable since that would be the only way they'd get into QuickBooks when I export the approved time. Non-billable items don't get exported from Time into QBO.

Lastly, I double-checked that Automatically show suggested transactions was checked, and it is. None of these suggestions has worked.

Interestingly, if a client has more than one time charge, and I convert one of them to an invoice, it allows me to add the other to that new invoice as expected. But (for years) it's been allowing us to add these time charges to existing invoices and that functionality needs to be restored.