Does it flag for copyright? I normally just copy-paste the lyrics into Suno, just to see how it would make the songs. They don't sound the same so I'm guessing they don't have that many songs in their copyright checks.
They definitely scan uploaded audio files for copyright. It's not comprehensive and I'm sure people work around it by slowing songs down, altering pitches, etc. (the same way people used to get around copyright detection on Youtube).