Learn Hardcore Korean: hoeuiga kkeutnamyeon baro toegeunhalgeyo. - When the meeting ends, I’ll leave work right away.

회의가 marks 회의 (the meeting) as the subject of 끝나다 (to end), which is an intransitive verb (it happens by itself). So 회의가 끝나다 = the meeting ends.

회의를 끝내다 (transitive) would mean to end/finish the meeting (on purpose), so then 회의를 would be possible.
회의는 would set the meeting as the topic (contrast/emphasis), e.g., 회의는 끝나면... = As for the meeting, when it ends...

What does -면 mean in 끝나면?

-면 attaches to a verb/adjective to mean if/when. In this sentence it’s naturally understood as when (a real future condition):

끝나다 → 끝나면 = when it ends / if it ends
It often implies “after that condition is met, then …”.

Is 회의가 끝나면 the same as 회의가 끝난 후에?

They’re close, but slightly different in feel:

회의가 끝나면 = when the meeting ends → highlights the condition/timing, often with a “right then” sense.
회의가 끝난 후에 = after the meeting has ended → more purely “after,” less conditional.

With 바로 (right away), 끝나면 sounds especially natural.

Why is 바로 placed before 퇴근할게요? Can it move?