This is one way of accomplishing it but probably not the only way. To make this I created a vector around the joint area and then digitally machined that area with a .75 inch ball nose and a fine step over (1%). I digitally machined the rest with a .250 ball nose and a fairly fine step over. I then created an outline with .375 inch radius fillets and cut out the model from the background. After double clicking on the waste material I was left with this preview. Under the modelling tab there is an option to create a component from the toolpath preview.
Thanks for the responses. I used a 2 rail to make the tenon, including the fillet on top. It worked fine but the I didn’ like how it looked ad scrapped the fillets. I forgot the component from preview tool. Thanks. I will try to remember it.