Good morning,
I want to start a Spring project with ionic, my goal is to publish the ionic app in the Google store and consume the backend with Springboot, I know you have to consume this backend by Heroku.
But I would like to know if uploading the App to the store would have me consume this backend on a private server, or local ...
Heroku has no influence on back-end services. It's just a way to host your Java / Spring application.
For the mobile application, what matters is the routes of services provided by the backend.
If you have a domain of your own, you can set it up wherever you want (including Heroku) and then call the services from there. That way, it does not matter if you use Heroku or a server of your own. The important thing is that the routes that the mobile application requests are correct.
For example:
If you have the domain meudominio.com.br and you have a back-end user registry service, your mobile application would call a route as:
https://www.meudominio.com.br/usuarios
This is independent if the backend is in Heroku or local, as long as your choice is set correctly.
However, you do not need a private domain, but in that case, the route would change depending on the hosting you choose: Heroku will have to provide something like nome-da-sua-app.herokuapp.com , the location would be an IP, Amazon would have another way on.
Of course, it is much easier for you to upload a Spring Boot application and configure the domain for Heroku than if you want to do it on your own server (unless you have knowledge below).
From what I understand you would have to publish the two applications. The application in the google store and the backend with web services on a server that supports the spring boot. With the backend published you would be able to access it from anywhere.