Credentials in Google developer console not loading

For me, it was the Disconnect chrome plugin.

[late edit: Other answers imply that this can be caused by browser extensions and / or security proxies (which often come with anti virus or firewall software). Please check whether you have an adblocker/privacy tool/etc. enabled - disable temporary and then try again. If this doesn't help, continue reading...]

Sounds to me like this could be resolved by filling the OAuth consent screen

https://console.developers.google.com/project/<yourprojectid>/apiui/consent

You'll need at least a product name and the email address filled. Google recently made a change so that you cannot create credentials as long as the consent screen is not filled. Before that change one often got cryptic errors during oauth, so this change actually makes sense.

If that doesn't help i recommend setting up another project and do a quick test with that project. Sometimes a project is not properly setup at Google in which case you'd need to contact Google's customer support.

In my case it was Chrome uBlock extension that prevented some JS scripts to be loaded resulting in infinite loader animation.