It’s not outdated, just because the Principled BSDF looks different.
The core concepts of CG/3D being taught are timeless, the changes are Blenders UI and additional features/tools in the software.
Never think of the latest version of Blender as the only version to use, this is a fundamental mistake, especially when learning.
Studios and professional artists will continue with older versions of Blender if it suits the needs of the project with particular features, tools or behaviours.
And would not change version mid project, even if the latest new shiny version is released.
