A News Piece of News

"A piece of news" is not a common phrase.

It's said that Greta Thunberg, a Swedish activist, is sailing to Gaza to raise international awareness of Israel’s ongoing war in Gaza and to break the country’s blockade on humanitarian aid.

The way I have corrected it would be equivalent to "the news piece said"

When I heard some of her opinions, I just felt that she needed to go to college to learn more and think more deeply.

There is a little bit of ambiguity with the way this is constructed. It could be understood, as far as I can tell, two ways:

1. You felt that going to college would help her learn more. You also felt that going to college would help her think more deeply.

OR

2. You felt that going to college would help her learn more. You also felt that she needed to think more deeply.

If your intention is (1), the ambiguity would be resolved by adding "to" before "think."

If your intention is (2), the ambiguity could be resolved by flipping the order, like "...I just felt that she needed to think more deeply and go to college to learn more."

I hope the difference in possible meanings is noticeable.

Maybe bravery is the real crucial one.

Others have pointed out that "the real crucial one" could be changed to resolve an issue, but you could also do something like this. In your previous sentence, you could say:

Today, after seeing too many heartbreaking photos and videos over the past two years, I realized that knowledge is not as important of a thing (or "of a quality") as I thought.

If you did that, then this "Maybe bravery is the real crucial one." would be acceptable. (I think changing it this way--by changing the previous sentence and keeping this one--would carry a more reflective tone.)

I read a news piecarticle on Weibo this morning.

"News article" is more natural than "news piece" in this context.

It' is said that Greta Thunberg, a Swedish activist, is sailing to Gaza to raise international awareness of Israel’s ongoing war in Gazathere and to break the country’s blockade on humanitarian aid.

Write "It is" instead of the contraction "It's" for more formal tone.
Avoid repeating "Gaza" twice; use "there" the second time to improve flow.

This news made me think a lot.

Or: "This news gave me a lot to think about."

A few years ago, this girl talked a lotGreta Thunberg often spoke about climate change.

“This girl” sounds a bit casual and distant. Since the subject has already been introduced by name (Greta Thunberg), it's more natural and respectful to either use her full name again or just say “she.”
“Talked a lot” is casual. Replacing it with “often spoke” makes the tone more polished and academic.

When I heard some of her opinions, I just felt that she needed to go to college to learn more and think more deeply.

Remove "just" to make the sentence more concise.

Today, after seeing too many heartbreaking photos and videos over the past two years, I realized that knowledge is not as important as I once thought.

Replace "too many" with "many" to sound more neutral and formal.

Maybe bravery is the realtruly crucial onequality.

"Truly crucial quality" is clearer and more formal than "real crucial one."

I hope she will bestays safe, and I hope that everyone in that place is safe too.

"Stays safe" sounds more natural, and "too" adds a smoother connection.

It's said that Greta Thunberg, a Swedish activist, is sailing to Gaza to raise international awareness of Israel’s ongoing war in Gaza and to break the country’s blockade on humanitarian aid.

"It's said that..." is technically correct, but it would be more common in English to just write "The article said that" or "It said that". The way it's originally phrased, "It is said that" would be slightly more formal.

Maybe bravery is the real crucial onecharacteristic.

Using the pronoun "one" here doesn't work, because you hadn't written anything before now to explain "one what?"