External libraries? What do you mean by that? External storage?
The last time I looked, Immich can’t work with a existing file and folder structure without importing (copy) everything in his own structure (database). That’s a big no go for me.
In Memories, the file structure of your photos is preserved as-is. And you can run it alongside with other solutions that respect your folder structure.
EDIT: looks like Immich can work with external folders. But: Does it put pictures from my phone in that external folder or in its own folder?
Immich on mobile doesn't give you much flexibility with where each local folder gets uploaded to yet so it doesn't preserve folder structure. If you're using the CLI you can program the structure and tell it which album a folder can map to.
You can add any folder to immich as external library. No need to use cli.
So if you want custom structure, synchronize files from mobile to server in any way you prefer (Syncthing, PhotoSync, etc.) and add that folder as an external library.
This is quite a basic feature which should be inbuilt to the Immich mobile app. It's a common use case to want your screenshots, WhatsApp media album to not be displayed on the main timeline.
If you're running an instance for less technical users it's more hiccups to setup syncthing etc and have to explain why another app is needed.
The last time I looked, Immich can’t work with a existing file and folder structure without importing (copy) everything in his own structure (database). That’s a big no go for me.
In Memories, the file structure of your photos is preserved as-is. And you can run it alongside with other solutions that respect your folder structure.
EDIT: looks like Immich can work with external folders. But: Does it put pictures from my phone in that external folder or in its own folder?