I have a Flask web application which is hosting in Google Cloud Run which is hosted with

This means that all of the redirect uris you try to add to your project. Must be HTTPS and not HTTP you can also not use localhost

As you are trying to use http://mydomain.run.app/authorize you need to change it so that it is https://mydomain.run.app/authorize note that the first one was http:// and not https://

The error is coming because your application itself is trying to send a redirect uri of http and not https. You need to fix your application so that it is using https.