This has indeed been requested quite often, but OpenAI already offers the Assistants API for developers who want to integrate their solutions into an app. In fact there are many options available.
I think it’s important to understand that ChatGPT is intentionally designed as a closed ecosystem, and if connecting to a custom GPT via an external API were ever possible, it would very likely not be free or included in a basic subscription.
So yes, it is possible, but highly unlikely, given the existing options available to developers.
Hope this helps!