Señor Gargoyle, this helped me a lot.
I swirl in darkness wondering how things work.

Over on reddit there's a great big flap about Adele being sued for plagiarizing some Brazilian artist's song. Her tune is similar to his, not exactly the same. Her chords are the same as his, altho they are elaborated differently. The mood of the two songs are quite different: his rejoices, hers laments. The lyrics of the two songs have zero in common. A Brazilian judge has issued an order for her recording co. to stop selling copies of her song and recall every copy they have ever sold, anywhere in the world. I don't imagine he has any authority over what happens in the US or UK or Japan or anywhere outside of Brazil, but he did it anyway.

The whole subject of copyrights on music is a puzzle to me. And this throws some light. I still don't see clearly but it's good to have some data.

A similar lawsuit against Ed Sheeran was dismissed after he explained that the chord progression at issue has been used many, many times over years. Actually, over several centuries.

An interesting facet of this was the mention of the work of Damien Riehl and Noah Rubin; they used a computer to generate all possible tunes of 12 notes in 7-note scales, and placed them all in the public domain. Someone claimed that since then (2019), "in the US, all lawsuits claiming musical plagiarism against the original artist have failed". This sort of goes along with my feelings; I mean, Yumpin' Yiminy, of all the things that should be free, isn't music number one?