And the even better one is thatMore interestingly, all of this new knowledge is very useful for my main job.

MORE NATURALLY: More Benefits from theMy Charity Yoga Classes

A few days ago, I wrote (an entry) about the yoga classes I taught to senior ladies.

NOTE: You can delete "an entry" from this sentence.

This course is part of a government-led project（How could I express this: the project itself is not for or from the government but it's under the government's healthy living program for older people）public private project, so one of the benefits is that the government offers me a free course about elder education.

NOTE: It sounds like a public private project (政府和社会资本合作). See https://zh.wikipedia.org/wiki/政府和社会资本合作

This course includes geriatric education and information about the psychology of aging.

MY GUESS: When I finish ithat program, I'll get a certificatione from an local education department.

And the eEven better one is that all of, this new knowledge is very useful for my main job.

I'm gonnaN STANDARD ENGLISH: I'm going to try harder to teach those ladies.

NOTE: In casual slang, the word "gonna" ... in standard English "going to" is more common.

A few days ago, I wrote an entry about the yoga classes I taughtam teaching to senior ladies.

"Am teaching" is better since you still teach the class.

If you haven't read it yet, you can find it here: https://langcorrect.com/journals/when-you-do-something-good/ ¶
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Now I am receiveding more benefits from this charity activity.

This course is part of a government-led project（H (how could I express this: the project itself is not for or from the government but it's under the government's healthy living program for older people）), so one of the benefits is that the government offers me a free course abouton elder education.

suggestion: ...of the benefits is that I'm able to attend a free government-provided course on elder education.

Is the government is delivering the course, or are they paying for an educational institution, such as a university, to provide the course to you?

When I finish it, I'll get a certification from an education department.

"From an education department" feels a bit odd because it's ambiguous. I can't tell if you mean a department within a government, or a department at a university or private school.

And thean even better one is that all of this new knowledge is very useful for my main job.

Suggestion: And even better, all of this new....

A few days ago, I wrote an entry about the yoga classes I taughtam teaching to senior ladies.

Since your yoga courses are ongoing, you should say "I'm teaching" rather than "I taught".

This course is part of a government-led project（How could I express this: the project itself is not for or from the government but it's under the government's healthy living program for older people）, so one of the benefits is that the government is offersing me a free course about elder education for the elderly.

When I finish it, I'll get a certification from anthe education department.

And the, even better one is that, all of this new knowledge is very useful for my main job.

If you haven't read it yet, you can find it here: https://langcorrect.com/journals/when-you-do-something-good/ ¶
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Now, I've received (or I've experienced) more benefits from this charity activity. (or act of charity)

This course is part of a government-led project（ (How could I express this: the project itself is not for or from the government but it's under the government's healthy living program for older people）), so one of the benefits is that the government offers mesubsidizes a free course abouton elder education for me.

Here's how I would express what you said in parentheses:

The project falls under the government's initiative (or campaign) for healthier living for older people.

And thean even better onebenefit is that all of this new knowledge is very useful for my main job.