In Customizer > WooCommerce > Product page – Components you can find 2 toggle options called “Enable text Before/After “Add to cart” Button” eg: https://d.pr/i/2ecMWf . If you’ll enable any of them, a text editor will pop. Inside these editors you can pretty much add whatever you want, but most importantly you can add global sections, by their shortcode.
Here’s a quick video – https://d.pr/v/ydBnFY . Basically you can create a generic global section, and inside it add button elements that would link to a modal.