Math. I'm embarrassingly bad at math, like can't do it in my head, don't get the math meme jokes, can't add fractions even on paper bad. I took 3 remedial math classes in college before they let me take the one that actually counted for credit. Just thinking about doing math gives me anxiety. I know I could get all sorts of better-paying jobs if I was better at it, but it's like my brain refuses to learn it beyond the basics. I really envy anyone who's good at it.
There are specific learning disabilities around math. If you think your issue might be something fundamental about how your brain works, you should look into dyscalculia
I have this and I always struggled with math. I was terrible at mental math and I wanted to be better. I changed all of my clocks to military time so I had to do a very small and easy mental math problem if I wanted to know the time. I started to get better at it and now I am better than most people I know (not by a whole lot, and it does still take me a while to get more difficult problems done). I now enjoy trying more difficult problems just for fun. I also developed some interesting methods to chunk problems in my head so they are easier to manage.
It's not about hours of practice. Small incremental changes over time can be a better way to go about it.
I'm the same way. I just had to keep trying to figure it out, and eventually something clicked. I'm still bad at doing math in my head, and I found out that different types of math math more sense than others. Like I'm really bat at algebra and calculus, but I can get geometry and trigonometry. It just took WAY more practice for me than other people I know.