I can't personally vouch for the program as I have not attended, but the University of Illinois offers quite a few mathematics courses online geared toward high school students, distance learners, and those preparing for grad school.
It is self-paced, so may not be what you're looking for, and it is expensive ($1250 if you have a BS already), but I seriously considered going this route before deciding to save big $$ and attend the local community college (which was actually a decent decision).
Program link: https://netmath.illinois.edu/
They offer 2 linear algebra courses, Math 257, which is Linear Algebra with Computer Applications (likely the "easy" applied version) and Math 416, Abstract Linear Algebra. Some of these Netmath courses do not have online lectures, but the Abstract LA course has video lectures from 2016.
From their site: "Math 416 is a rigorous, abstract treatment of linear algebra. Topics to be covered include vector spaces, linear transformations, eigenvalues and eigenvectors, diagonalizability, and inner product spaces. The course concludes with a brief introduction to the theory of canonical forms for matrices and linear transformations."
When I was investigating what to do in order to solidify my math credentials (still a work in progress), I knew UofI was a good school, and figured credit in one of their courses (online or not) would not be a terrible investment. At a bare minimum it wouldn't be belittled or untrusted like other online certificates might.
Plus the credit should transfer anywhere, if that's important.