If you go to Jamstack.org, one of the most popular websites that for "Everything JAMStack", you will find over ~80 different headless CMSs listed on their website (https://jamstack.org/headless-cms/).
Here is my how I classify them so it is easy for you to understand and pick from:
Almost all of the have some API enabled. However, most of them have a terrible "filtering" system. So if you want filter shirts for Men and Women in Red, you will have to most likely send a request for Men's shirt in Red, Women's shirt in Red and then combine the results.
A few of them (such as PIMCORE https://jamstack.org/headless-cms/pimcore/) are proven product information management solution and can cover fairly complex requirements, Including MEDIA management.
Most of them are general purpose platforms with no real edge. They are basically some back end + REST API or GraphQL engines and you can do what you want with it. Examples are DATOCMS. Of course, these are the least agnostic solutions and a lot of them are available in hosted or open source edition. You can do whatever with it.
About half of the 80 or so CMSs are open source. Most of them have a GraphQL or REST API with a back end included. Most of them are heavily developer focused with JSON mentioned as features.
I tried to check what are some differentiators in closed source that has the potential to make it special. Some of them such as DATOCMS provide CDNs, produce Videos, Modular Blocks and Dynamic Layouts stand out as worth paying for it. Some of them have basic workflow to move your post/content from draft to published with a few steps in between.
So how to go about selecting a correct CMS? Well, it depends where you are in your enterprise. If you have an ERP system, if you have a dev/ops team that can handle complex deployments, multiple integrations then one of these above can do the job very well. Some are more capable and some give you all the room you want to grow.
However if you are a SME / Startup, you still need to evaluate accounting system / develop portals / develop signup flows / develop stock / inventory management or for some even have a manufacturing system. That is a lot of different things to develop starting from the scratch. You will run out of budget / or your runway would be too small to accomplish this without deep pockets or getting a VC as your sugar daddy.
ERPNext is an upcoming full features ERP system that has close to 50k deployments across the world. It comes with 800 odd REST API end points with filtering options. It can do accounting, stock, manufacturing, cost centers, run multiple companies, run multiple finance books, run multiple projects. It comes with Socket IO, Redis Caches. Some one also has built a GraphQL App to go with it.
So if you are a SME or a startup with some advanced requirements to manage accounting, stock, manufacturing AND are looking for a solid headless CMS, ERPNext could be really viable options.
You are fully future proofed. And you can always get anther Headless CMS to go with it in the future. But this light weight Framework and Application has already lauched a thousand ship, including India's LARGEST discount broker with ~4M users.
I promote ERPNext as an ERP system and implement it as an alternative to Salesforce, SAP and Oracle. You can check us out at https://www.grynn.io