The definite article usage in a sentence

Please have a look at the sentence below:
This is the popular song of Taylor Swift.

To me, if there isn't any specific song related to that singer known as "popular", the usage of the here is not correct.
The refers to the construct "popular song" here but more to the word "popular". And since apparently there isn't such a specific song known as "popular", we should use an indefinite article: This is a popular song of Taylor Swift.

Using the definite article can be optional in some cases but in this sentence, it's not.

Do you guys agree with me?

Answer

I agree with you (in the absence of additional context) that the sentence should read,

"This is a popular song by Taylor Swift."

However, if one asked, "What are you listening to on your headset?" the answer might be,

"I'm listening to the popular song by Taylor Swift called, 'You Belong With Me.'"

This example confirms your observations of where the definite article could be used appropriately (i. e., in reference to a specific song). However, even in this example, like you, I would still prefer to use the indefinite article:

"I'm listening to a popular song by Taylor Swift called, 'You Belong With Me.'"