Enjoying music on Shabbat

Is there no enjoyment here from a Shabbat act? I mean the way someone who turned on the music turned on the speaker on Shabbat or plays the guitar on Shabbat. And is there a distinction between a Jew and a Gentile?

A Sabbath act is a different issue. There is no intention here and it depends on whether it was done for me, accidentally or not, etc.

Does the fact that there is no object here excuse me in any case?

No. This is a disagreement among the poskim, but they include it as a branch. I personally am not sure that there is no hafza here, because in my opinion, a device that works is a new hafza (therefore the operator is moving from a builder).

I don't understand. When they say there is no object here, do they mean that the sound is something that doesn't really exist? Or something else?

There is no substance in the sound. This is also what Maimonides writes in his book, Ha-Ha'aretz, about the shofar being a source of forbidden pleasure. However, here he is talking about a sound created by operating an electrical device, and it is possible that it is pleasure from the device that is created here, and then it is indeed pleasure from the object of a prohibition.

Now I thought that light is also something that doesn't really exist, and still no one says there's a side to enjoying the light of a candle that someone else lit for me.

Indeed. And apparently according to the method of the living, a person who only desires is forbidden, one should say that a burning candle is a desire, or that fire is a desire (even though light is not). According to the first method, an electrical device that has been turned on is also a burning candle. According to the second explanation, fire is a desire, so there is no analogy with the sound that comes out of an electrical device.