But nowhere did it say if you are able to disable all comments in a specific gallery after the images have been uploaded. Has there been any update to this in the recent WordPress updates?
There hasn't been a recent update on that. Because of how images are saved and how galleries are currently just a list pointing to several images that each have their own separate comment settings, it's not likely this is something that will be changed in the near future. I like the suggestion though! I'm sorry it's not something that will probably be updated any time soon.
Your best bet for now is to either edit each image from Media > Library and change the comment setting for each one separately or go to Settings > Discussion, turn off the "Allow people to post comments on new articles " setting temporarily, and re-upload the images all at once so none of the images have comments enabled from the start.