True, but if you research lots of sources and still emit significant blocks of verbatim text without attribution, it’s still plagiarism. At least that’s how human authors are judged.

Plagiarism is not illegal, it is merely frowned on, and only in certain fields at that.

This is a reductionist take. Maybe it's not illegal per se where you live, but it always have ramifications, and these ramifications affect your future a whole lot.