Tira here to help.
Depending on the theme you are using, when a variant is no longer in stock, there will be an “out of stock” image showing that replaces the “Add to Cart” button on the product’s page. Here is an image from my test store of what this looks like:
Is this something that you would want to do? If it is, could you let me know what theme you are using? If not, I would love to see an example of what you’re looking to do so that I can provide you with guidance or resources to help.