Free intermediate tutorials?

I have PBI Free desktop on Windows 10.

I have done about 5 tutorials from the Microsoft site but they seem very basic, especially when it comes to calculating columns. I seem to be doing more intermediate stuff now but I have not found any tutorials that covers intermediate stuff. For example, my last question was answered with using the DIVIDE function. I should have found a tutorial that covered that but I have not.

Is there a Youtube channel or another site with more intermediate tutorials that are free? These are my only resources I can use to learn PBI. Your answers have been every valuable to helping me learn and I have been taking lots of notes from your answers.

Thank you!

EDIT: Some of the things I'm doing is I have a matrix. I have 2 columns which sum numbers by department and cost center. There is more than one cost center per department. I have to subtract these 2 aggregate numbers (estimated minus actual) in the matrix.

Also, executives want to see a black vertical line separating some columns. I did not see any options to do this in PBI to, for example, have one column use a rule to the right of it.

I'm not yet doing analysis of sales over time. I might do it in a month or so.