If you were OK at school mathematics, but did not study a STEM subject at university, you may be interested in these resources. They are designed to help students prepare for a university mathematics admission test. They take a broader approach to understanding and problem solving in mathematics than the school curriculum.
The Open University: distance learning in the UK
MathsChoices: the choices available to study Mathematics by distance learning.
To understand much about modern science requires a reasonable level of mathematics. Without some appreciation of the mathematics, the explanations are incomprehensible. The difficulty for many of us is that we dropped sciences and mathematics because they were too hard to understand at the speed required to complete a curriculum. I don’t doubt that, given enough time and good materials, an educated person could eventually understand enough. But if that time were more time than required to complete a curriculum, then it is probably a non-starter.