As for plagiarism, it may get the user into legal problems, but I think that articles on sites like coinbase/Binance are open source but you need to check about information.
While their article is open (everyone can read it without register an account), it can't be classified as open source since Binance Academy mention "© 2022 Binance Academy. All Rights Reserved." at bottom of the article. But even open source content have license with certain requirement and limitation such as proper attribution.