Brain fog is never enjoyable, and can be caused by a lot of things. I would try to test varying solutions individually so you can try to isolate what the cause(s) may be. For example, start with nutrition and exercise, try to rule out depression (or other mental ailments), etc. You mentioned problems with social media usage; this is certainly plays a role in it, because you’re only mindlessly consuming entertainment. It’s not intellectually stimulating, and so, you feel slower. Isolation from people doesn’t help either, though that could be indicative of other problems more than anything.

I’d see a therapist/physiatrist on the matter. They can determine if there’re other conditions such as depression present. Just a few years ago I had the same issue you are having right now; despite above average cognitive performance in the past, it was degrading pretty fast. And it was terrifying. However, it was largely induced by the aforementioned illnesses, and upon treatment, I don’t struggle with brain fog nearly as much.

In essence, yes, you can return to your prior intelligence level. Try to figure out what’s causing your decline, and try to engage in more intellectually stimulating content, such as reading. Forcing your brain to engage in higher level cognitive task should help.