In QuickBooks Online (QBO), we can only make certain sections or fields bold for invoices, deb137.
Currently, the option to selectively bold individual words or phrases within free-text areas like the description or terms fields is unavailable. However, QBO allows you to customize the font style, size, and color in predefined areas such as headers, labels, and totals using the Custom Form Styles feature.
Also, please check out this article for guidance in recording invoice payments in the program: Record invoice payments.
If you have other queries about invoices in QBO, reach out anytime. We'll always be here to assist you.