Can I have a headless Shopify setup with different payment processor?

Hi, I have an ecommerce store where I’m migrating a fully custom website built on Next.js and Supabase to be Next.js for the front end and Shopify for the backend.

I’ve seen mixed answers on whether you can use a custom checkout along side Shopify’s admin capabilities (inventory, orders, product management) and was wondering if I could get some more clarification on this. Is it possible to use my own custom checkout with my own different payment processors (Heartland / Paypal)? With Heartland I will not be going to a separate page for payment processing.

I’ve seen that you HAVE to use Shopify’s checkout. I’ve also seen that you can use their backend systems while building a completely custom front end including checkout.

What have y’alls experience been with this?