I started to learn OpenGL a few months ago and it is the recommended library to learn because most of the steps in the pipeline are already managed by OpenGL itself. You still need to code some steps but nothing too complicate, even to render a basic triangle in Vulkan is cumbersome so at the same time is easier to screw up and then understanding the root cause in the pipeline since you have to do a lot of stuff by yourself.
I started to learn OpenGL a few months ago and it is the recommended library to learn because most of the steps in the pipeline are already managed by OpenGL itself. You still need to code some steps but nothing too complicate, even to render a basic triangle in Vulkan is cumbersome so at the same time is easier to screw up and then understanding the root cause in the pipeline since you have to do a lot of stuff by yourself.