I answered a similar question here:

• Can't configure a consent screen. Clicking on "OAuth consent screen" redirects me to "Google Auth Platform / Overview"

In short, many believe it's an issue with rolling out the new UI, and some were able to fix it through a combination of

1. using a different browser/private/incognito)
2. Deleting and re-creating the project
3. Use a login link that redirects to the oauth consent screen
4. If the app is for external audience, set yourself as a test user

None of these actually worked for me though (my app is internal), but worth a try - I recommend subscribing to the below in case a fix is reported:

1. https://www.googlecloudcommunity.com/gc/Community-Hub/Problem-with-Oauth-consent-screen/m-p/913303
2. https://www.googlecloudcommunity.com/gc/Google-Cloud-s-Observability/Cannot-access-OAuth-Consent-Screen-setup-keeps-redirecting-to/td-p/908771
3. https://www.reddit.com/r/googlecloud/comments/1l3zi9q/help_google_cloud_console_redirects_me_from_oauth/
4. https://www.reddit.com/r/devops/comments/1isamvc/cant_configure_a_consent_screen_clicking_on_oauth/
5. https://community.home-assistant.io/t/google-drive-oauth-consent-screen/842720