Which songs are plagiarized and not covers?

Let's start with the definition of music plagiarism, 8 bars of similarity in music is considered plagiarism. But 8 bars means consecutive syllables and not the total similar syllables that add up to the whole song. Or three quarters of a syllable in each bar is plagiarized. Getting back to the point, what songs are actually considered plagiarized in this definition? For example, Cai Jianya's "Red High Heels", Liu Ruoying's "Later", Yu Kewei's "Time to Boil Rain", and so on. It is worth saying that the arrangement and composition of a song is and the original person is the same, when the song is not your arrangement or composition, but will mark themselves as original, can be recognized as plagiarism.