It's almost certainly not because you're actually getting dumber...and it could be burnout...but, what you are probably facing is probably something more on the axis of philosophical-existential questioning, which tends to rear its head periodically with age. A line of work can be logically good to pursue but eventually your body and emotions will fight you on it if they aren't feeling nourished.
Like, you've had it good in terms of career, from a simple percentiles-income standpoint. And most likely you have had a lot of moments of satisfying problem solving. But the learning of the job is basically done now, and it's just reframing of the same ideas as new technologies. It's like being told that the words in English are going to be renamed tomorrow so you had better get started on learning them.
For right now, punch the clock, and take up an immensely challenging and deep hobby like music or painting if you haven't done so already. If you find that the hobby pulls you forward where the job doesn't, then the path forks: "work to live"(keep punching the clock and moonlight a little) or "live to work"(either turn the hobby into the new career, or turn this into a reason to challenge yourself with tougher coding problems that go beyond learning another framework)
Like, you've had it good in terms of career, from a simple percentiles-income standpoint. And most likely you have had a lot of moments of satisfying problem solving. But the learning of the job is basically done now, and it's just reframing of the same ideas as new technologies. It's like being told that the words in English are going to be renamed tomorrow so you had better get started on learning them.
For right now, punch the clock, and take up an immensely challenging and deep hobby like music or painting if you haven't done so already. If you find that the hobby pulls you forward where the job doesn't, then the path forks: "work to live"(keep punching the clock and moonlight a little) or "live to work"(either turn the hobby into the new career, or turn this into a reason to challenge yourself with tougher coding problems that go beyond learning another framework)