As mentioned elsewhere in the discussion they now provide a way to migrate data from one iPhone to a another, but that's assuming that you have the old device still.

I have an old device which I have saved because the messages on it are emotionally important to me, but that device is too old to transfer to my new device.

Main problem being you don't have access to the file structure on an iphone. So you can't simply drop a backed up folder in there like you can on Android. You are stuck needing the previous device.

Since iOS 12 or so, iPhone has a built in files app. Every app can integrate with that. So when I create a file (let’s say chat backup) in app A, I can put it in the files app. Then in app B (or app A on a new phone) I can easily open that file from the same files app.

Even before that every app got a documents folder that was shared between the app and iTunes

iOS has had a Files app for years, locally. You could easily export an encrypted .zip from Signal and save it locally, just like how Signal on Android saves it to your internal storage.

For some reason, the Signal devs won’t even acknowledge this possibility and continue to say “we can’t enable iCloud backup” - which is fair enough, but nobody is asking for that and they’re simply putting their fingers in their ears.

Buy why can't they enable iCloud backup? What's so bad about uploading an encrypted blob to the cloud.