I'm sure the ...

I give up.

... that starts out your "answer" doesn't help. That would be a big, red flag to reviewers that it might be NAA (not-an-answer).

And I have to agree that, even with frustrated comment removed, it's really not-an-answer in this case, as it was written.

Negative answers are absolutely acceptable, but they shouldn't come from the OP of the question unless you've determined the cause of the problem and can explain it. Here, you posit that:

This problem seems to simply be due to differences in behavior between a linux ext4 filesystem and a MacOS APFS filesystem.

Which is true, but you didn't know, and you couldn't explain why.

You could (and probably should) have, edited your original question to ask:

Could this simply be due to differences in behavior between a Linux ext4 filesystem and a macOS APFS filesystem?

The accepted answer, on the other hand, documents the reason for this behavior. It's still a negative answer, but with the supporting details needed to make it useful.

The rest of your "answer" consists of either "comments" or information that should have been edited into the question:

• Please read "NOTE" in my original question

  A comment, replying to someone's comment. Not part of an answer.

• Per the suggestion below, I re-installed rsync via homebrew ...

  Things that you've tried in order to solve your original problem should be edited into the question, even if they were comments on an answer.

Thanks for bringing this here to Meta. This is absolutely the right course of escalation. Sometimes the community is going to agree with you, and other times it won't, but you've made a good argument above. Unfortunately, I have to say I personally disagree with you in this case, for the reasons below.

For starters, I'm sure the ...

I give up.

... that starts out your "answer" doesn't help. That would be a big, red flag to reviewers that it might be NAA (not-an-answer).

And I have to agree that, even with frustrated comment removed, it really was "not-an-answer" in this case.

Negative answers are absolutely acceptable, but they shouldn't come from the OP of the question unless you've determined the cause of the problem and can explain it. Here, you posit that:

This problem seems to simply be due to differences in behavior between a linux ext4 filesystem and a MacOS APFS filesystem.

Which is true, but you didn't know, and you couldn't explain why.

You could (and probably should) have, edited your original question to ask:

Could this simply be due to differences in behavior between a Linux ext4 filesystem and a macOS APFS filesystem?

The accepted answer, on the other hand, documents the reason for this behavior. It's still a negative answer, but with the supporting details needed to make it useful.

The rest of your "answer" consists of either "comments" or information that should have been edited into the question:

• Please read "NOTE" in my original question

  A comment, replying to someone's comment. Not part of an answer.

• Per the suggestion below, I re-installed rsync via homebrew ...

  Things that you've tried in order to solve your original problem should be edited into the question, even if they were comments on an answer.