Currently, business central doesn't send tax information to Shopify on product/variant export.

The Tax information on shopify's end is simply a boolean field on whether to charge tax. This can be sent through the same API used to update the prices and variant information on shopify.

It can probably work by using the price validation business central does to send the prices to shopify currently, which can probably work when the price is calculated, if the VAT amount is 0, the charge tax field can be false, otherwaise true.

You can put a field in the Shopify Shop card as well to give more granular control over the features to make things simple for users who what to manage taxes separately within the 2 systems.