Do I need to pay porkbun extra to use a domain with proton mail?

I'm new to this and feel so in over my head with all the information, sorry for the newb questions. I'm hosting on Squarespace, registering domain w porkbun, and want to use the domain on proton mail (unlimited plan). I'm confused by porkbun's information on this, https://porkbun.com/products/email , where they say I need to pay extra to use the domain with email, and more for use with Proton. But I haven't seen anyone else mentioning paying extra to use their domain with Proton. Will I need to do this, or can it be done through Squarespace hosting, or something else? Thanks.