I am plain stupid. Is there anyway to change that?

sudo go see a therapist, asap!

And as david927 wrote:

In my opinion, consider trying several therapists until you find one that works well for you; they vary significantly.

Personally I think you shouldn't strive for the usual career, money, big house, many friends or whatever people commonly consider 'successful'. Life has only the meaning you yourself give it.

You might be better served seeking creative activities, maybe volunteer jobs where you act as buddy/support partner for others, (community?) gardening or whatever. Or something totally out there like go on a continent-crossing hiking journey.

This planet is big; life's too short to see & do everything. So regardless: do less of what makes you not happy, and do more of what does. But 1st go seek professional help.

Your problems have solutions. It sounds like these mistakes were repeated and clear. It seems that you could intellectually see it, but you chose differently for other reasons. It may be an emotional barrier. Do people consider you stubborn? If so, that's fixable. Stop. You don't have to brain up, you have to wise up. The thing in your way is you and your brain but not in the way you're expecting; it's not intellect but wisdom. And it's not going to be fixed with brain surgery or an increase in IQ. It's going to stop when you allow it to stop.

People think of Therapists as Surgeons, a last resort. But they're also General Practitioners that you can just talk to. It can be that external help/voice. I really suggest trying for a couple months and see if it offers you anything. No harm if not. Or don't -- that's ok too. But they can't do shit unless you try.

Try the two other things I mentioned: long walks and wild writing. Again, try it for two or three months. If it doesn't help, no harm.

The key to this is in your hand. But it may not fit the lock that you're expecting. If you're open to true change, you can be pleasantly surprised but first you have to try.

I really appreciate your praise but writing doesn't determine intellect or cognitive capabilities. And either way, LLMs have made writing redundant which means it's not something that is a good sign of human creativity or intelligence.

That right there is what I am talking about! You at least tried to create something, it failed because of other factors, not your intellect; it may have failed bcoz it ain't easy to promote a dating site without (VC) money.

I did not want to reveal this because I feel very ashamed even thinking about it: you are probably at worst a decent programmer who makes decent money working as a developer/engineer. There were two different fields I have been really interested in: Physics/Chem and Technology. With Physics/Chemistry, I tried to learn the fundamentals well, even bought a kit to experiment with, but due to a combination of not putting enough effort, erroneously thinking I can start learning later and still be better than others due to my misguided thinking that I was smarter (lol), and many times not being able to understand a lot of abstract scientific concepts that are important fundamentals, I was unable to become adept or good at Science. Moving on to tech, the same thing happened with me procrastinating, not putting in enough effort and finding it difficult to learn to code and understand technical concepts. Even little kids are able to code cool shit up and here I am not able to be consistent or smart enough to ever become good at it! I have always felt there was something off about me, my intellect, dexterity and ability to understand the world. I consoled myself by daydreaming and thinking I was smarter and can become better by working hard but I never did the hard work. Now, when I look back, I can clearly how badly dumb I was and am.