I’m not aware of a way to do what you’re asking, but you can move your music library to an external volume connected to your Mac, and then sync it to your device.
That volume could be a USB stick or if you have an SD card slot that would work.
https://support.apple.com/guide/music/change-where-music-files-are-stored-mus69248042d/mac
Apple also offers a subscription service to sync your music library to the cloud and then sync it across your devices and save storage space.
https://support.apple.com/en-us/108935
Also, if already you’ve ripped your CDs, where are those files currently stored? If it’s a NAS/networked volume, simply:
- mount the volume
- turn off the iTunes/Music setting “Copy files to Media folder when adding to library”
- import music
This will keep your music on the other volume, and you can still sync with your devices as long as that volume is mounted when you do it.