all of my downloaded music on itune is not showing in my library, only purchased music showing up

Did you just setup iTuners on a new computer? If so, did you transfer your iTunes library:

Move your iTunes library to a new computer - Apple Community

or

Back up and restore your iTunes library on your PC - Apple Support

Do you have an Apple Music subscription? If so, see:

If songs are missing from your music library after you turn on Sync Library - Apple Support

Just got my Iphone 7 replaced and can't sync music from my IMac...What do I do? Songs that I have recorded in Garage Band which were transferred to IMac playlists aren't found on My Iphone7... Very upset...All help appreciated.

If I understand your issue, perhaps the 'If you use a Mac' section in this article will help:

If your computer doesn't recognize your iPhone, iPad, or iPod - Apple Support