Depends on your target platform and what you're doing. On Windows? Learning DirectX will be more bang for your buck. Apple? Then Metal is probably the way to go

Depends on your target platform and what you're doing. On Windows? Learning DirectX will be more bang for your buck. Apple? Then Metal is probably the way to go, if you need low-level control and performance. Vulkan if you want crossplatform low-level control. If you don't care so much about the nitty gritty details and want to get things done quickly, Unreal or Unity is probably more rewarding. One of the difficulties with OpenGL is that it's awfully fragmented and there are many ways to do things that have evolved over time. Learning resources are consequently spread around, and it's really easy to learn suboptimal obsolete ways of doing things.