Give a title name under bundle information 

Quantity as an Option is suited for bundles like "Box of 4", "Box of 6", "Box of 8" etc.In case you want create bundles like "Travel Set", "Skin Care Set" where customers can choose X products at each step (or category). <a target="_blank" rel="noopener noreferrer nofollow" href="https://app.tango.us/app/workflow/Setting-Up-the-Mix--Match-Bundle-in-Shopify--Without-enable-quantity-as-an-option--f652cfbd2a53459096b2243612a77126#step-cf4c9e81-7a59-4eb1-8ba4-7caa20884d75">Check out tutorial for "Quantity as an option" Disabled</a>

Check Enable quantity as an option

You can choose the title under "Quantity as an option"

Fixed Price: The price of the bundle is set at a fixed amount, regardless of the individual product prices or any other factors.Dynamic Price: The price of the bundle is calculated dynamically based on the individual prices of the products in the bundle or other factors (like discounts).

Select Fixed Price or Dynamic Price based on your requirements

Click on "Add Category"

Click on Create category and select products"

You can choose the products 

If you don't have any Add Ons/Free Gifts to pair with bundles, you can skip this step

You can click on Add Ons

Select products for Add Ons 

Choose Add Ons Settings 

Click on Save

Now click on "View Bundle in Shopify Admin

Click on Manage

Click on "Manage sales channels

Check Online Store

Select your theme as shown below 

Select Active from "Status"

Click on Preview

The preview is shown as below 

Creating a Mix and Match Bundle in Shopify (With enable quantity as an option)