Is there anything I can do to make myself more intelligent as an adult and not as a child?

I have tried to improve my mind by training myself in different ways, but is there anything else I can do?

I do not like endurance fitness, because I used to have a weak heart, which improved over the 4 years after the pandemic started, after I stopped working a physical job that was straining my body too much.

Is there anything I can do to make myself more intelligent as an adult and not as a child?
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