slim4-skeleton VS Slim

You can have the container call in a config folder with a file called dependencies or how ever you want. A few existing examples of this is here - Slim calls this app/dependencies in this skeleton project and Odan's Skeleton has this as config/container in their project.

Yes, as an example, the First Application's business logic (not that it's much) doesn't tie itself to the framework, as one example. Odan's Slim Skeleton, ADR Example (yes, I know you are the author), and the Aura Payload example class can be seen as other examples.

Even just the tests in your first link are very useful to see, such as: https://github.com/odan/slim4-skeleton/blob/master/tests/TestCase/Action/Customer/CustomerCreatorActionTest.php

Another option, to me and speaking to the OP as an alternative, it is simpler to add some Data Mappers/Repositories to abstract away the Database code. Good examples is the sample ADR application, Payload library example, Slim 3 First Application, or this Slim 4 Skeleton application

You could also use a Slim Skeleton like Odan's which incorporates much more features to help - docs.

Try Slim again. The setup may be too much, but the concept is the same. Look at the first application or any of the skeleton apps to help (https://github.com/odan/slim4-skeleton for one).

Slim is a micro PHP framework used for web development with 11.7k stars and 2k forks on GitHub. It has a simple and intuitive API development process. It is a micro-framework, meaning you only get a minimum of support for HTTP requests and forwarding requests to appropriate controllers. So the question is, why should you choose a micro-framework? Because it offers you flexibility and high extensibility.

Slim 4, a minimalistic PHP micro-framework, offers middleware support to easily add CORS headers. Middleware in Slim acts like a series of layers through which your app sends a request. One such layer can be responsible for adding CORS headers.

SlimPHP 3 Skeleton app shows this as well: https://github.com/slimphp/Slim-Skeleton/blob/3.1.8/public/index.php

How hard did you look? There are plenty out there. FastRoute, Phroute, based on FastRoute, with basic middleware, League/Route - routing with middleware, using FastRoute, PSR 7 & 15, Slim Framework, at it's core, it like League/Route, etc. None of these require a full framework to use.

You can have the container call in a config folder with a file called dependencies or how ever you want. A few existing examples of this is here - Slim calls this app/dependencies in this skeleton project and Odan's Skeleton has this as config/container in their project.

Maybe use this if you don't like to dive into bigger frameworks: https://www.slimframework.com/

Go for Slim: https://www.slimframework.com/