Just tried this and the following works :). Create a Text template variable and in it put your first variable, than
<br> (no slash) and than your second variable. If you use that as the Content of your ContentNote you get a line break in between the two varialbes
If you do use
<br/> the flow will crash when you run it. I hope your variables don't contain anything to exotic or the flow may crash as well.
This solution also works for formula variables. (Text templates don't allow formula expressions, so we can't make the break conditional using those.) So if you want to do this just use this in a formula and assign it to the Content of the ContentNote:
IF(ISBLANK(FormulaSalestarget), '', '<br>') &