For example, one of the best developers on my team (a little bit older than me) is "on the spectrum". We've worked together for nearly 20 years, starting at about the same time. Early in our career, we would dig into the details of APIs and patterns and be able to rattle off the details of the changes when a new dot release of an library came out.
As the years have gone on, I've "lost interest" in the details knowing that I can look them up when I need to and have naturally defaulted to generalizing ideas. That is, rather than knowing that we need to change the third parameter in the function call in FOOBAR 3.2 when we upgrade from FOOBAR 2.9 because the details of the memory management changed, I just know that we use the FOOBAR function because it does a specific task that we need.
The reason I bring up my friend/coworker is that he never generalizes, he gets stuck in the details. He can't design his way out of a paper bag, but he can write thousands of lines of code over the weekend with full unit tests and there's never any bugs. So we make a great team, he's one that has focused and has every detail at the tip of his tongue. But he never sees the big picture.
So I view getting older in software as (over) training AI. My brain works in the generalization route and the more I see, the more connections I make, but I need to "make room" in my brain by not encoding the details. My friend's brain works differently. He encodes details and can keep a deep call stack but at the expense of ever being able to see the big picture.
I guess that's a long way of saying that maybe you shouldn't be so quick to think it's cognitive decline. It could be just that your brain is encoding things differently after seeing so many examples in your career.
I know I'd fail miserably at porting an API now (I've done that when I was younger very efficiently). But I also know that I can bring a much higher level of design and ideas to the team than I could have 20 years ago.