who just come to SO with the intent to ask questions which generate knowledge as to benefit all.
Our purpose is to generate useful knowledge for all, yes. But consider the quality of your question.
You showed off a 2D array, where you loop over each element of that array with two
for loops, with each loop accessing a particular dimension of the array. You then asked us to explain how to loop over a single dimension of the array.
... I know that I've been programming for 30+ years, so I'm coming at this with a vast wealth of knowledge and experience at the task. But I genuinely cannot fathom how one can write 2D iteration over a 2D array, but be unable to convert it into 1D iteration. Even if you only got that code through copy-and-pasting from some tutorial, I don't understand how you can be unable to just play around with it and work it out on your own.
Asking on Stack Overflow is not meant to be the first recourse when you encounter a problem. You come here to ask when you have made a good faith effort to resolve that problem on your own. Whether that's looking in a debugger, just playing around with code, doing some Googling on how loops/arrays work, or whatever.
Can you truthfully say that you made a good faith effort to solve the problem on your own?
I would say that your question can not "generate knowledge as to benefit all"; it only benefits yourself, the person who is in this particular position. That is, most people who don't know how to iterate over a single dimension of a 2D array probably also don't know how to iterate over both dimensions of a 2D array. So your question won't help them.
It only helps yourself.
That, coupled with the fact that you probably could have worked it out for yourself if you took a little time to do so, shows that this is a low-effort question. That makes it worthy of downvoting.
Voting is not about you; it's about your post. Good content gets upvotes. Bad content gets downvotes. The vote total is about telling other people "this is good content; check it out" or "this is bad content; don't bother unless you like wasting time". They are a sign of a post's quality, which is of interest to other people.
People aren't downvoting your posts to harm you; they're downvoting them to tell others the quality of the content you provided.
This is not about being welcoming to a person; this is about being welcoming to bad questions. The former is fine; the latter is not.