I feel a lot of folks in these kinds of threads are wearing more tinfoil hats than anything I have seen. Even when Google scans your private emails its not this much conspiracy driven
So lets see
Is Apple creating a backdoor to Government ?
This Answer is entirely based on how you view it through practical angle or conspiracy angle. e.g. I trust Apple so I dont believe they are creating a backdoor and technology wise Its not a backdoor either because a Backdoor means Government having Keys to Secure Enclave even with iCloud Off, so logically it cannot be a back door if the hashes scanned locally is same as on iCloud and even if Apple wants it, the scope cannot be expanded due to Secure Enclave
Is Apple scanning images on your Phone before it starts uploading to iCloud
No, Apple is scanning HASHES or images not the images themselves when the transition starts FROM your Phone to iCloud. For example. The scan of the image hash will not occur if your internet is off because the upload has not begun as per documentation
Can Apple expand the categories for types of hashes to scan for iCloud Photos?
Again, this answer is entirely based on how you view it. From a conspiracy angle or practice angle. Apple has stated that they will not and I trust their word. Else I would not be buying their products.
Can Apple scan your phone for non-cloud data?
No.
Why not scan hashes on iCloud servers alone like other tech companies ?
Again, this answer is entirely based on if you view from conspiracy angle or practical angle. Apple has stated that it does not want to scan iCloud libraries because that is more intrusive than scanning hashes locally one by one as opposed to all the files in iCloud. Again, personally I trust their word on this from a technical perspective than most security experts who are looking at it from a functional perspective