While Shopify apps are accessible via Shopify’s app store, they are hosted on the developer’s infrastructure. This means you can host your app on any developer hosting platform and build it with the tech stack you are most comfortable using. This gives you the freedom and flexibility to use whatever tech stack and coding language you or your app developer prefers.
How you go about setting up your app depends on your app goals, framework, and preferred programming language, and your technical lead should help you here.
Shopify hosts libraries for Node, Ruby, and Python, and there are several other libraries maintained by Shopify community members.
YouTube is also a great resource for learning how engineers go about building Shopify apps in a particular programming language and tech stack if you have an interest.