Flask landing page with Shopify web store
Yes that's possible, but has nothing to do with Flask.
You can set your A record of website.com to point to your Heroku server.
For the Shopify part, I am not familiar with how exactly you set this up on their site, but they have a documentation where you can learn how to set up a subdomain (e.g. shop.website.com) to use with your Shopify shop.
Is it possible to have a website where the landing page is a Flask app hosted through Heroku, connected to an online store that is hosted through Shopify?
For example, website.com is my Flask landing page. Then shop.website.com is a Shopify store selling my products.
If possible, what do I need to do?