The wonderful day

TheA day that makes me feel like it is a wonderful day is thea day when I can apply what I think.

It happened between the 21st and 30th, when I felt energized, and as if everything was under my control.

I could decide what I should do, clearly and simply.

I hope that I can reach/achieve that kind of day again.

"Reach" doesn't really make sense here (at least to me), and I think "achieve" gives the same effect as "reach"

The wonderful day

The day that makes me feel it is a wonderful day is theIt will be a wonderful day when I can apply what I think.

From the rest of your writing, it sounds like you're saying "It will be a wonderful when I can carry out my plans for the day."
You've got a good sense of the meaning behind "apply what I think" in that you're expressing the difference between what you plan versus what you do.

I usually make a plan that I need to execute for the day, but I rarely doexecute it well.

However, I have experienced such a dayday like that before.

"such a" sounds very lofty, poetic, formal.

Maybe it was because my dopamine levels had recovered through a dopamine detox.

It happened bBetween the 21st and 30th, when I felt energized and as if everything was under my control.

I'd recommend combining the previous sentence and this one:
Maybe it was because my dopamine levels had recovered through a detox, but between the 21st and 30th, I felt energized and as if everything was under my control.

I could decide what I should do clearly and simply.

I hope I can reachhave that kind of day again.

The day that makes me feel like it is a wonderful day is the day when I can apply what I think.

I could decide what I should do clearly and easimply.