> You will never get the same quality of fundamental material

If you're looking for fundamental material, the last thing you want is learning a very (not slightly) outdated and weird API.

> Vulkan and DX12 are currently flawed APIs that are unnecessarily complex and doesn't even match the performance characteristics of current-gen hardware

And OpneGL is worse

> And OpneGL is worse

I disagree. OpenGL is truly bad, but there is no API in this world as bad as Vulkan.

> If you're looking for fundamental material, the last thing you want is learning a very (not slightly) outdated and weird API.

I've never seen a more detailed tutorial than LearnOpenGL that actually goes through the concepts of graphics programming thoroughly and actually make things other than just "learn how to use the API". That alone should be enough to cement the site's longevity.

> And OpneGL is worse

It's never late to learn Vulkan / DX12 after learning learnopengl.com! The value of learnopengl.com isn't in the APIs, it's about learning the basic concepts of graphics programming. If you start learning with Vulkan without any prerequisite knowledge, you'll be bogged in low-level details from the start that isn't really related with learning the actual fundamentals. (And you'll probably have to unlearn Vulkan and DX12 again once a new API has surfaced)

Have you actually read the linked site beyond its name? The site is about fundamentals. Yes, it contains OpenGL code, but what it covers is the fundamentals of real time graphics, not just OpenGL API.