I didon't thoughtink that it's really hard to write every day about something new.

This sounds more natural, if you mean to say that you feel confident you can write every day about something new.

I decided to share a post every day here because I have to improve fast.

replacing "fast" with "quickly" would sound more polished, but this is OK

I want to think, create and write, but it's not that easy.

You could consider using the oxford comma like this:

I want to think, create, and write, but it's not that easy.

But why I'mam I writing these things?

In question form, it is "am I" instead of "I am" or "I'm."

I usually struggle with keeping myself motivated and maintaining a continuous workflow, so this writing practice is a little daily task that helps me to keep working on my goals.

I would suggest either:

1. I usually struggle to keep myself motivated and to maintain a continuous workflow...

OR

2. I usually struggle with keeping myself motivated and maintaining a continuous workflow...

"a" is used to indicate a singular noun

instead of "I see dog," it would be "I see a dog"

In addition, it helps me improve my thinking in English, my writing skills,and grammar skills, and another important things.

This sounds quite natural. I revised the list because it seems like you have three things in focus:

1. your thinking in English
2. your writing and grammar skills
3. other important things

instead of the original version:

1. thinking in English
2. writing skills
3. grammar skills
4. other important things

I don't like being corrected, and if someone highlights my mistakes., it's frustrating and confusing.

combined with the next sentence

It's frustrating, and confusing.

With this practice, I constantly get some of these inputs, amnd I get used to it.

the prepositional phrase "with this practice" needs a comma since it comes at the beginning of the sentence and is followed by a pause when reading it

And for that I have to find new topicas to write about, so I need to broaden my horizons.

Day 11: Don't Ggive Uup, but Kkeep Uit up!

I know that we generally capitalise most words in a title, but when a title is a full sentence like it is here, I find it makes more sense to capitalise it like any normal sentence. You will see news articles do this as well.

I didn't thoughtink that it'sd be really hard to write every day about something new.

"Didn't thought" is not grammatical. Generally in compound verbs like this one, we change only the first word when conjugating: "don't think" → "didn't think".

I decided to share a post every day here because I have to improve fast.

But why I'mam I writing these things?

I usually struggle with keeping myself motivated and maintaining a continuous workflow, so this writing practice is a little daily task that helps me to keep me working on my goals.

I rephrased the last bit of the sentence so that it sounds more natural.

In addition, it helps me improve my thinking in English, writing skills, grammar, and another important things.

(1) "Improve thinking" on its own might sound a little awkward. I think "improve my thinking" sounds better, at least in my opinion.
(2) When you say "another important thing", the reader would expect you to explain what it is, since you deliberately singled it out. To remove this expectation, you can use "other important things" instead, which is less specific.

I don't like being corrected and if someone highlightsing my mistakes.

With this practice I constantly get some of these inputs, amnd I get used to it.

And for that I have to find new topica to write about, so I need to broaden my horizons.

Good use of the idiom "broaden my horizons"!