Option Click / Photoshop 2021 / MacOS Big Sur / Wacom Graphics Tablet

I was having the same issue that many others seem to be having as well. None of the suggestions given worked. My "option key" on my keyboard kept bringing up "Could not use the clone stamp because the area to clone has not been defined (option-click to define a source point). I finally found my solution. 

I use a Wacom Pro M. So I looked at the Wacom settings and one of my Express Keys was assigned as the option key. I used the Wacom Express key instead of the keyboard on my MacBook Pro and voila it worked, for both healing and clone. So, if you use a graphics tablet, give this a go and see if it works for you.