So I was trying to do it in a calculated value and did not see the function in the runtime functions list. So I then tried doing it with a single line and noticed that it has inline functions which does include that function.

Hi, so this works in the preview mode of designer for my form.  But when I create a new item, the panels that should be disabled, based on the rules, are not disabled.

Any thoughts on how to trouble shoot this?

So further investigation on this, you have to put the SharePoint group name within quotes.  So this is the way the formula would look:

fn-IsMemberOfGroup("FacilitiesRequisitionCapitalPurchaseApprovers")

Some of the unlisted inline fuctions still work if you type them in with the fn- prefix.

That bit of information was incredibly helpful!  Thank you!