Shopify's product information can register up to 100 variations by combining one to three items, but if there are many variations, it can be a hassle to check each one. It is a hassle to create a list for each product, but it is also a good idea to use Liquid to generate a list of combinations and post inventory information.
How to display inventory list for each variant on the product details screen (also supports irregular variants where not all variants exist)
[How to set it up] Add a custom Liquid block to the product information of the product template and insert the code
