https://www.mathacademy.com/

Don't pay too much attention to the "is it AI" claims, afaik they don't use AI to code the site or make the exercises. It's a mastery-estimating learning system that keeps track of how well you understand prerequisite topics to show you the next one you can easily learn to extend your knowledge. You want to do their math foundations sequence and then you can go on to multivariable calculus or methods of proof. Focus on building an intuitive understanding of the topic, if you do a review of the topic for example you can click "review this topic to brush up" and go over to the lesson and try to encode the things you forgor into your memory from a different perspective. Intuitively understanding the math visually is a good starting point to aim for.