Hey ATP,
So from what I understand you want to offer Pickup and Shipping for the same product. Does the product ship from the same location the pickup is at? Either way you’ll want to go into the Shopify admin settings and enable “Local Pickup”.
Then at checkout the customer will be able to pick “Pick Up” or “Delivery”.
If the inventory is at two separate locations you might want to look into an app that syncs inventory across two products, or add local pick from X location as a Shipping Option rather than the official “Pick Up” in the settings.