Linear Algebra for Everyone
math.mit.edu
math.mit.edu
I hope I am not getting downvoted to hell but I always thought Strang was overhyped. I watched his lectures and bought his book and I never felt this is the most accessible way of teaching LA. At least not in the way, people hyped it up to be.
I much prefer Jim Hefferon's LA book for example. No hate towards Strang but I always felt so dumb when I watched or read his stuff after people were raving about it.
I wish I had a recommendation for you.
It's not an open source textbook and there's no linked discussion.
There is a set of video lectures that outline it: https://ocw.mit.edu/resources/res-18-010-a-2020-vision-of-li...
(I took these in 9th grade)