Oh I'm not looking for another job. I just miss having short term goals and structure. I feel as though I peaked early and I have the highest degree in my field...for me it just feels like I'm in 'work until death' mode.
I just miss learning and shit.
You're not stupid so I'm sure you know this already but you can get that structure and short term goal feeling from other things. You likely won't get structure from online courses anyway.
I don't have any real solid "go do this" advice because honestly its going to be a personal thing but if you took up a solid fitness routine or self taught skillset a natural structure would fall into place.
Shitty example but it's the best I have. I decided years ago I'd learn how to cook and bake, not just be able to make a cake and a decent meal but like cook everything, It was born out of necessity but I had an actual passion for it. Short term goals were simple, produce good tasting food, and its structure was great because I'd be "forced" to cook at least once a day to keep with social norms (3 meals a day). Cooking is one of my favorite things to do but I've found it really rewarding.
You can better yourself academically sure but don't limit yourself to just that. Think of it as you have the job part down now work on being a better person all round. People spend years getting to the point you are now and you're still pretty young all things consider so reap those benefits.