It sounds like you're referring to Hatsune Miku , a very popular virtual singer. Here's a bit of context:

Who is Miku?

Hatsune Miku is a Vocaloid software voicebank developed by Crypton Future Media. She is represented as a 16-year-old girl with turquoise twin-tails and is a virtual idol. The voice is synthesized from samples of a real singer (Saki Fujita), but Miku herself is not a human and does not "sing" in the traditional sense. Instead, her voice is generated by software.

Why "can't sing"?

• Hatsune Miku does not have a physical voice or vocal cords ; she is a digital avatar.
• Her singing is produced by Vocaloid technology , which uses recorded voice samples and algorithms to create singing.
• Because she is a software, she cannot sing live or naturally like a human singer.
• However, many producers and fans create songs using her voicebank, and she has performed in concerts as a hologram, delighting audiences worldwide.

In short, Hatsune Miku "can't sing" on her own because she is a virtual singer powered by software, not a real person. But thanks to technology and creativity, she has become a beloved and influential icon in music and pop culture!