linuxjourney.com : Linux Journey is now part of LabEx and will remain a free, open-source, community-driven learning project.

linuxcommand.org : CLI tutorials (Command Line Interface)

linuxsurvival.com : Tutorials designed to make it as easy as possible to learn Linux CLI (Command Line Interface)

readthedocs.io : More CLI, because you can do far more from the CLI

server-world.info : Copy and paste build-a-server instructions, let's you easily compare similar tasks in different distros.

ryanstutorials.net : Are you seeing a pattern? CLI is the way to go...

billdietrich.me : Good general info with a lot of comparisons between different sub-systems

coursera.org : Red Hat specific courseware

https://www.coursera.org/specializations/oss-development-linux-git

https://www.coursera.org/specializations/c-programming-linux

https://www.redhat.com/en/services/training/ex200-red-hat-certified-system-administrator-rhcsa-exam

https://www.redhat.com/en/services/training/all-courses-exams