Fees are created as products in your store. The method for controlling tax settings depends on whether you're using a Function fee or a Block fee.
How to update tax settings on a Function fee:
In your Shopify admin, go to Online Store > Apps and open Magical Fees.
To edit an existing fee, find it in your fee list and click to open it. To create a new fee, click Create fee.
In the Calculation section (where you set the fee price), locate the Charge tax on this fee checkbox.
Uncheck the box to stop taxes from being applied to this fee, or check it to apply taxes.
Click Save.
Note: Order fees applied to the total order amount cannot be taxed and this setting will be automatically disabled.
How to update tax settings on a Block fee:
In your Shopify admin, go to Products.
Search for the fee by name, or filter your products by Product Type "Fee."
Open the fee product you want to update.
Under Price, uncheck Charge tax on this product.
Click Save.
This will stop taxes from being added to your fees.