I'm presuming you already know how to use computer and business applications adequately.
One business course is unlikely to increase "job opportunities." But I would suppose that if one had accounting or finance understanding that would be seen as margnally better than none.
If you wanted one course to make you a better employee, I would suggest Critical Thinking. Anything that can help you reframe a situation, structure a process for problemsolving, and then do so would increase your performance immensely.
A business ethics course will help you understand if the business is operating in a just and sustainable fashion, or else help you recognize the signs that it is time to leave before the indictments start coming.
But just starting out, I think the familiarity with the accounting and financial vocabulary and ideas will be a help to at least communicating with the "other side" of the business.
I think these ideas will apply regardless of country, but I don't think that I've been to yours.
One final tip, what is it that you wish to be known for? What is the thing that "makes you, you?" That is, "how you add value to whatever you do?" What do you wish to be known for?
In my case, as a foreman, I was Safety first guy. I wanted noone hurt. As I learned more, I kept that but became the "Quality guy." Not only was noone going to get hurt, but we weren't going to produce bad stuff either.
These made me learn how to be an effective trainer, and to practice what I preached.
Those two and a hell of a lot of process knowledge got me up into the front office.
So what is it that you are "all about?"
milo
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People say between two opposed opinions the truth lies in the middle. Not at all! Between them lies the problem, what is unseeable,eternally active life, contemplated in repose. Goethe