Hey there!
There are many types of art such as painting, photography, sculpting, playing an instrument, singing, dancing, and more. If art has a visual subject, it is something that has to be seen to be enjoyed.
When thinking of an answer to this, we need to think about what type of art we could enjoy without being able to see. If you were blind, could you enjoy the Mona Lisa? Well, no, because you cannot see it!
What about a photograph, sculpture, or fine architecture? You would not be able to enjoy that?
Even at a dancing performance, you cannot see any of the dancing going on, so all of these so far have a visual subject.
However, if you aren't deaf, you can listen to things if you are blind. You can listen to an instrument or someone singing, and all of these are music! You cannot see music that is created (unless it's the actual sheet music but that's not necessarily what we're talking about!), but rather, you enjoy it by listening to it!
Therefore, music is the type of art that has no visual subject!
I hope that this helps! Have a wonderful day!