Replace All Case Insensitive Based on Incoming Value

Hello. I am having some issues getting “replace” to work the way I want; kindly have a look.

This works:
$Name.replace(/ron/gi, “Ronald”)

So does this:
$Name.replace($OldName, $NewName)

But, I want the above to also work with the “gi” option but it does not, e.g.:

$Name.replace(/$OldName/gi, $NewName)

Has anyone handled this before? If so, kindly share your solution. Thanks.