iPhone 16 Pro with 1TB storage running out of memory on device and in the iCloud

I found this article about the 100.000 songs limit, that can be saved in iCloud, no matter how much space is available on other devices that use Apple Music:

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Access your music library on all your devices

If you subscribe to Apple Music, you can make your entire music library available on all your devices when you’re signed in to the same Apple Account and you turn on Sync Library in Settings. You can access your library any time you’re connected to the internet, or even offline, if you download your music.

Your music library can keep the following available in the cloud:

• Up to 100,000 songs, not including songs (or music videos) purchased from the iTunes Store; files can be no larger than 200MB

• Matched songs (songs available in the iTunes Store, whether or not you purchased them there) at iTunes Plus quality (256kbps DRM-free AAC) and other songs at their original quality

• Music videos purchased in the iTunes Store

• Playlists that include songs and music videos

• Smart Playlist rules, which are applied on the computer or device they’re downloaded to

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copied from: Access your music library on all your devices - Apple Support

Did you check, if the files using up your storage space on your iPhone and in iCloud have an identical categories?

What's the difference between device storage and iCloud storage? - Apple Support

Check your iCloud storage on any device - Apple Support

You don't say what "nearly full to capacity" means--how nearly full is it? if iCloud or your phone are very close to full, they may not be able to manipulate the files-- even deleting files becomes problematic when the storage is full. You might think about buying more space on iCloud for a month while you straighten things out, and then you can go back to your previous setting. I notice that there is no 1TB plan for iCloud, so it's not clear what you have.

As for the storage on your phone, you may need to dump some apps. Removing apps helps a bit, but you can also remove apps and their data, which will help more.

Have you tried a forced restart on your phone? 

Force restart iPhone - Apple Support

This is different from a simple Power Off. I had to continue holding the button down past the "slide to power off" message, and then I released the button only after  the Apple Logo appeared indicating a re-start. 

Do I understand this right? If you leave it on None, then you don't keep any of your songs (for long, anyway) on your phone, so you depend entirely on the internet. So every time a song changes, you need to wait a moment while the phone gets it from iCloud.

If you set it to 128 GB, they you keep around 25000 songs on your phone, and if you want a new song that isn't one of the 25000, then the phone reaches out to iCloud and swaps it out with some songs that you haven't listened to in awhile. That's what it sounds like…

It looks like your track average is more than the usual average of 5 MB/song, and you average more like 8 MB/song. So those numbers imply that for you 128 GB would hold maybe 16000 songs before swapping would occur.

I think if I understand all this correctly, then you just have to decide how often you want to wait an extra few seconds while a song loads. I think. I would want to keep 50 GB free to all for easy swapping of files.

I decided apple.com is a always take a good dicesation

I've asked for this post to be moved to Music on Mac, since there are likely folks there more expert in the Music Library.