(high speed layout, BGAs, etc)
Not free, but not super expensive and they also have introductory courses ($50).
https://academy.fedevel.com/courses/online-want-to-design-yo...
The most important talk for beginners getting into high-speed is probably this one: https://www.youtube.com/watch?v=ySuUZEjARPY because without proper grounding, interference and EMI is going to destroy your HF signals (for example CPU to RAM bus).
The long-term answer is that you'll eventually want to try all of them. In my opinion, half of PCB layout is tool-agnostic and the other half is getting fast/proficient at a specific tool.
When I moved to Altium, I knew that I wanted to "pour copper" to make a power plane, so I just had to google what the Altium equivalent was. The PCB concepts of layers/routing/grounding/clearance/vias/stackups and all that are universal, the terminology and shortcuts are just changed between tools.
If you just want to start doing some projects, KiCAD is mature enough and you’ll find more tutorials and content.