This sounds like you added some extra options when setting up the consent screen that put you into a category of requiring verification. Make sure you aren’t entering too much and following the instructions exactly and not doing more than is stated.
I had to do the following to get it to work for Google Drive
After setting up the client and the OAuth credential,
From APIs and Services section (Search for it in the top bar if you can’t find it),
on the left hand menu click “OAuth consent screen”, it will redirect to Google Auth Platform / Audience,
on the left hand menu click “Audience”,
Under Testing, click “PUBLISH APP”
Click Confirm