I don't understand why this functionality is not available without workarounds, digital products are as popular as physical ones. Of course there is possibility to use other services for that, but if you're paying for squarespace website and it has a shop option, it just does not make any sense to do that.
Here are the features digital product makers need:
Customer can set the price themselves. And you could set the minimum as 0 or higher.
Possibility to add digital product variants with different prices, just like for physical products. These could be different licenses or different product versions that include or do not include certain assets.
How is this not obvious?