Create Rule in Magento 2.4 If a combined $X amount of items in Y category, then get free ship

I have been searching for days, but cannot find a way to do this. Open to getting an extension to pull this off if you know of one.

We want to offer a coupon code.

If you have $100 or more of products in X Category(s), then get free shipping.

Our challenge is that we use flat rate shipping ($15) as our default option (with Fedex for faster options)

I have been unable to find the right combination of rules and shipping settings to make this work.

Test 1

Under Rule Condition

If ALL these conditions are TRUE:
|  If an item is FOUND in the cart with ALL of these conditions true
|  |  Category is one of 20, 21
|  |  Price in cart equals or greater than 100

Actions

If ALL these conditions are TRUE:
|  Category is one of 20, 21
|  Price in cart equals or greater than 100