Both the Roku and iPad/iPhone Spectrum apps have a setting you can change to switch between alphabetical and numerical listing of channels. Default is alphabetical. Does the Apple TV not have this same setting? I ask because I don't have Apple TV, but I woul d think this setting would exist across all apps especially since it is on the iPad/iPhone app. Again I don't have Apple TV so I could not tell you where to look for this setting, but maybe another forum member knows?
Well unfortunately, if there is no setting to change, all you can do is wait for Spectrum to get around to updating the app and fixing the problem. As a long time user of the Roku and iPad versions, you could be in for a long wait.
I have the Apple TV 4K with Spectrum TV app, and yes you can sort by channel number. See bleow.
Push the Menu button once on the Apple TV remote to pull up the guide:
Now use the track pad and move to the left to hightlight the 'dots' on the left:
Now, hold the track pad down to pull up the guide options, here is where you can set the sort options and filter options. As you can see, you can sort by Channel Number: