I have an iphone with 256 GB of storage but I cannot use it for downloaded music. Why not?

so you are downloading music from the music app or previously purchased music with the iTunes app?

you don't allocate memory specifically for music. if space is available, it can be used for music.

if you go to settings, general, iPhone storage you can see what you have available on your phone and it will categorize all your storage. You can also see how much space each app is taking up.

if downloading is hung, make sure you are connected to wifi.. maybe do a hard restart on your phone

https://support.apple.com/guide/iphone/force-restart-iphone-iph8903c3ee6/ios

no, you don't have to have an Apple Music subscription to download music you already purchased.. I was just responding to the question you asked about how/where to see the 'optimize storage' option.

I would suggest again (not sure if you tried it after I originally suggested) to try a hard reboot of your phone.

Then if you think this is related to storage space, go to settings, iPhone storage.. give it a minute to load everything up. Does your phone show plenty of available space?

Are you connected to a good wifi signal? You may have to change something in settings if you are trying to download over cellular data.

Now that the phone has been rebooted and you're on wifi.. can you try the download again?

Also curious, are you attempting to download from the iTunes app or from the Music app? I subscribe to Apple Music so I can download from either place..

I am on iOS 13.5.1 using an 11 Pro and for me it is exactly where your screenshot shows it is. I'm guessing that you have to have the iCloud Music Library switch toggled on/green in order to see this setting?

Downloaded from where? What error message do you get?