Ok. I tested the module by myself. Google changed some policies, so the guide of README.md in the module is somewhat outdated.

Here is a simple fixture;

Selection of Application type on Create OAuth client ID should be Desktop app not TVs and Limited input devices and others. (Step 7 of the guide)
When generating the token,

the browser will open and then ask for some consent. (Despite of warning for test/unverified app, do it anyway. You can remove that warning by your app is published.). But after confirmation, the page might be directed to ERR_CONNECTION_REFUSED error page. Don’t panic and see the URL of that error page. It would be something like;

http ://localhost/?code=4/SOME_HASHED_CODE_OF_YOURS...&scope=https://www.googleapis.com/auth/photoslibrary.sharing…

Copy the marked portion of your browser, then paste it into your terminal.
(Step 10 of the guide)

Boom, it will work.

However, I think the module has become legacy and need updating with recent skill. I hope I have some time to upgrade it.

MMM-GooglePhotos ;Google OAuth Developer