menehar

It does. But it also means that if you want to reset the tracking you would need (for every app) to also clear the storage of the app and logging off and log back in with a different account before starting to use the app again

You can for older devices (so your app has to target only those I think) but with added permissions that you will definitely question It seems it is more complex or impossible now: https://developer.android.com/training/articles/user-data-ids#mac-addresses

I didn't throw rocks at Material You for being an actual privacy leak but just thinking about the fact that it gives a reason for users to want to use a custom wallpaper instead of default or unicolor I woild have fell for it if I was not already aware of that WallpaperColors API

Material You is a privacy issue. It gives a reason for people to have a custom wallpaper.Because of the WallpaperColors API, any third party app can use the wallpaper to generate a unique ID based on that

Is lemdro.id just a frontend? Is it not attached to a particular instance?

it's better than NIST who previously certified an elliptic curve with mathematical weakness to offer them and NSA a nice backdoor