Personally, I think it is plagiarism, because you really need to give credit for what you are quoting. But I understand this might be polemic and not everyone agrees.

IMO this is one of those things that is going to have to be looked at on a case by case basis.
And how are do you want to go with it, partly because the quoting feature of this forum is meh at best

You raised an interesting question, as I also see several users who think that simply quoting is enough to ensure that the post is not plagiarized.

It should be enough to not get the user banned.

No, all you need to do is to not claim that you created the text. Quote tags do that.

If you put something in quotes, it's quite clear that you are not pretending that the content is originally yours. However, you are still not giving credit to the person who wrote it. So you put yourself in a grey area where you probably won't have any problems

You are not a beginner to ask a question like this, so if someone put something in the quote it will certainly not be considered plagiarism, as far as I know it never was.

Here is an example that I reported as plagiarism, and which stood unhandled for as long as 8 days, until I posted it publicly, and the user subsequently edited the post. If it wasn't plagiarism (and obviously global mods/admins think so), then what you have doubts about has nothing to do with plagiarism (by forum standards).

Likewise, in parallel with your question, I would like to ask if the font in the copied post is changed and the post has no source, is that considered plagiarism?
This is plagiarism at best.