Khan academy might be a good starting point.
On youtube you can watch hundreds of their
short videos on subjects like
algebra, calculus, probability, linear algebra etc.
When you feel like you master that material
you can move on to MIT OpenCourseWare on youtube.
Gilbert Strang's Linear algebra.
David Jerison's Single variable calculus.
Denis Auroux's Multivariable calculus.
Tom Leighton's Mathematics for Computer Science.
They also have courses on probability, statistics,
differential equations etc.
Other personal favourites, which i actually liked more than MIT, are these
Discrete Mathematics. Arsdigita University. Instructor: Shai Simonson
The Fourier Transforms and its Applications. Standford. Professor Brad Osgood
Probability Primer. Mathematicalmonk's channel
General topology from the very basics, including set theory, techniques for proofs
Graph theory by Sarada Herke