To make text bold in forms that allow use of HTML, you must use what are called 'Bold tags' that are constructed as follows:

<b>This text will render as bold in a form that allows HTML</b>

To explain further, you must start by adding an open bold tag, then insert the text between this open tag and the close tag that will be made bold.

Open tag: <b>
Close tag: </b>

E.g. I only want <b>this</b> word to be bold. (In the example, only the word "this" would appear bold)

There is a third party resource that explains this in greater depth -

Please note that if you build your form using HTML, we do not directly support any issues this code may cause, so there is a risk in using it.