@ Shopify team We want to integrate Shopify application to our new ecommerce project.
Whether we can develop Shopify application with client theme.
Can application host in On-Premise
Shopify does not offer an on-premises plan, nor do they host your application for you on-premises.
To integrate shopify into other platforms see Custom Storefronts, Marketplaces, or Sales Channels
https://shopify.dev/custom-storefronts