I'm like you, having some troubles applying math to solve actual problems and quickly forgetting what I learned. And I feel most people are like that (I don't actually know) but some make it look like it's easy to them because they have lot of practice or experience with that problem. For example, Casey worked on Granny 3D
which is an animation software, so he had to learn and use matrices a lot (I guess).
As you say it comes down to practice, and until you have to use some math to really solve a problem, and do that several times it will not feel intuitive. I also feel like I'm missing some basic intuition or confidence about simple high school math thing and I often end up working them up in my head or on paper to make sure it's right.
One thing I started to do last year is to keep a notebook with things I learn (math, programming, music...) which I can quickly refer to. I try to make those notes as complete as possible, which often includes things I didn't get right away and what made me get it. If I encounter a similar problem for which I know I have some notes, I look them up, hopefully solve the problem, and complete my notes with new information from solving the problem a second time. I started that last year, it helped me a few times (not an incredible number of times) to solve problems but it's also useful to refresh your memory about basic things. For instance my notebook first few pages contains notes on basic math (calculus) to which I often refer to make sure I understand a bigger problem.
I also use symbolab
when I don't understand the result of solving an equation in an article. It shows lot's of the steps in solving the equation and the rules used. It's not perfect but it can help.