I've gone back and forth trying to decide whether or not I have aphantasia, mainly because like you internal sounds are so vivid for me and it's not at all the same for my visual phenomena. But after doing visualization practices as part of my meditation practice I think it's something I've gotten a lot better at. Often in vajrayana buddhism you'll be given some visual object to meditate on (a buddha, mandala, a river flowing, fire, etc) and at first there is a lot of discursiveness to it while you're meditating: the trees look like this, the river is flowing this way, the shadows are here, etc. Then that sort of dies down until (for me) a very vague image starts to appear. It's in a different space than where my eyes would produce an image, it's more dream like, and you sort of just let go of paying attention of visual phenomena that arise at your closed eye space and go to a more immersive dream space where you're sort of in the scene itself.
But maybe I have aphantasia and am totally wrong!