Syncing iPhone - Music and iTunes confusion - Mac OS Catalina

Just to confirm, I'm referring to the files stored locally (from CDs etc), not my iTunes purchases library.

I tried it and it started filling up my Apple TVs with everything that's on my phone, and had to roll it back. There was no option to choose what to download.

I wish Apple were less vague about how iTunes/Music integrate and library propagation. One tick has the potential to cause a lot of damage to a local library.

Thanks Jimz, I've messed around with it more and understand what you mean now.

I didn't realise 'sync library' creates an 'iCloud library' storage area and then uploads the local library to it.

Well, I say it 'uploads the local library' but a lot of my content says 'Waiting' under iCloud status in 'Get info', and has done for days now.

I like the concept of consolidating my library across devices, but in practice it's a vague mess. I had to reset network settings on my phone to stop 'syncing library' whirling permanently, content I paid for has disappeared, content I didn't pay for has either uploaded, disappeared, moved/renamed or stuck in waiting.

Oh well, I should have known better really. Thank god I have a backup of my entire library on disk!