Add Donate next to Add to Cart button on Product pages

I have a similar question as @BOMMESTUDIO - I'm offering payment plans on certain products (not all products in my shop), and would like to put a button next to my "Add To Cart" button that links to my Payment Plan subscription product.

This is one of the products that I'd like to add the second button to: https://www.holdspacecreative.com/shop/andrea-squarespace-template-plus-copy

And here's where I want the second button to link to: https://www.holdspacecreative.com/shop/squarespace-template-only-payment-plan

Is there a way to apply a second product button to certain products?

Trying to achieve the same thing, or adding a donation section to the checkout would be good. Is there a way to connect the cart and the donation block?