المشي بعد الشغل منيح لما بكون زهقان.

Because المشي is a verbal noun, meaning walking as an activity.

So the sentence is built like:

Walking after work is good...

If you said بمشي, that would mean I walk / I am walking, which would make it a different sentence.

In Levantine, الـ is often used with general activities and familiar everyday concepts.

• المشي = walking in general
• الشغل = work / the job

So بعد الشغل is a very natural way to say after work.
It is literally after the work, but idiomatically it just means after work.

منيح is a very common Levantine word meaning good, nice, or beneficial/helpful, depending on context.

Here it means something like:

• good
• nice
• a good idea

It is not Standard Arabic. In MSA, you would more likely see جيد.

Because in Arabic, present-tense sentences like this usually do not use an expressed verb for is / am / are.

So:

• المشي بعد الشغل منيح
  literally: walking after work good
• natural English: Walking after work is good

This is completely normal in both Levantine and Standard Arabic.

Here لما means when or whenever.

So لما بكون زهقان means:

• when I’m bored
• whenever I’m bored

The second meaning often fits well, because the sentence sounds like a general habit or repeated situation.

After words like لما (when), Levantine often uses بكون to mean I am / I’m in the state of being at that time.

So:

• لما بكون زهقان = when I’m bored

Using بكون makes the clause sound more natural as a time-based situation.
Just saying لما أنا زهقان is much less natural in everyday speech.

In Levantine, the بـ prefix usually marks the present/habitual form of the verb.

So:

• بكون = I am / I’m usually / I happen to be, depending on context

In this sentence, it helps give the sense of a repeated or general situation:

• when I’m bored
• when I happen to be bored
• whenever I’m bored

Because Arabic often drops subject pronouns when the verb already shows who the subject is.

بكون already means I am from the verb form itself, so أنا is not necessary.

You could add أنا for emphasis, but in a normal sentence it is usually omitted.

زهقان usually means bored, but it can also mean fed up or sick of things, depending on context.

So it is a little broader than just plain English bored.

In this sentence, bored is the most natural meaning.

Yes. زهقان is the masculine singular form.

If a woman is speaking, she would usually say:

المشي بعد الشغل منيح لما بكون زهقانة

So only زهقان / زهقانة changes here, because it describes the speaker.

Because منيح describes المشي (walking), not the speaker.

So the structure is:

• المشي = the thing being described
• منيح = good

Since المشي is treated as masculine singular here, منيح is the natural form.

By contrast, زهقان / زهقانة describes the speaker, so that word changes with the speaker’s gender.

A few things:

• منيح is a Levantine colloquial word for good
• زهقان is a common colloquial Levantine word for bored / fed up
• بكون with بـ is typical spoken Levantine-style grammar

A more Standard Arabic version would sound much more formal, for example with words like جيد and العمل instead of منيح and الشغل.