Retrieving YouTube API v3 data for all my channels

Question

I have five YouTube channels that are all under one user account (one e-mail address). I can switch between them at will within the YouTube mobile app, YT Studio and so on by using the app's Switch Account function.

I also have developed some processes that will retrieve statistics about my primary channel's videos and store them into a database.

I would like to also retrieve the same information about all my other channels, but I don't seem to be able to do this. Those processes can see only PUBLIC information about the other channels. So unlisted/private videos are skipped, for example. The simple solution would be to create credentials for the other channels of interest and apply those new credentials to the processes, but I don't see a way to create credentials for any account other than the primary on the Google Developer Console

Am I missing something about Developer Console that would allow me to create other sets of credentials for the other channels? Or maybe there's a "switch account" equivalent I'm not aware of? Or what other solution is available for multiple channels?

According to this link, this is the correct forum for my question, but Google seems to be unresponsive more often than not.