I’ve had issues with IPSW update using my Mac before with my iPhone getting stuck in data recovery mode. Once it’s finished though the data is fully intact. This is the reason I only do OTAs these days.
Now if you’re using a genuine cable to update then it could be something else that terminated the connection before the update is finished. Another possibility could be a corrupted config which I always suspected in your case.
Now for some reason you’re obsessed with that stupid Apple Devices app but you should’ve at least made an encrypted backup before you updated. Hopefully, now you can start from scratch and your issues will go away. If you’d been cautious enough to make an encrypted or iCloud backup, you could restore using either of those and get most, if not all, of your data back and still be able to resolve some of your persistent issues.