I would recommend Shopifys APIs. Theres a lot to them, they’re well documented, and you can build a developers store for free.
Adobe commerce is another one. You can get a dockerized store up and running pretty quickly, also free and their documentation includes some basic suggested workflows.
Edit: these are mostly for practicing consuming apis, not sure if thats what you were looking for.
They didn’t have a Project 2025 game plan going in like they do now.