At a time when I didn't even think about getting a K-Pop fan, I already listened to J.Fla's cover versions on YouTube. She even made a song about her YouTube career.
In Western Rock music there are the Ukranian Youtubers Daria Zaritskaya and Sergey Sershen. They started as 'Sershen & Zaritskaya' with Rock cover versions. Now they produce their own songs as band 'Noapology'.
AFAIK Faouzia started at YouTube too. She was even called 'our little secret' there, because she already had a substantial fanbase (including me) there long before the music industry noticed her.
Leo Moracchioli is also a music producer (Frog Leap Studios). But don't take his cover clips too serious, first and foremost he wants to have fun. Nevertheless he's a good multi-instrumentalist, but maybe not the best singer.
And unfortunately he looks not nearly as good as Rosé...
Other YouTubers that got popular with cover songs, but make their own music now, are Halocene and Violet Orlandi. I visit their channels regurlarly.