I was helping my client create his own Google API key for a Google calendar for his website (I would now share mine instead).
When he clicked “Create Credentials”, he did not have the option to create a Google API key.
See the difference between client’s options and my options in the screenshot below:
I found a difference: he had “Google Calendar API” on left, while I had “APIs & Services” only.
I told him to click “APIs & Services” in top left (yes, that is a link).
And then I said to try again… “Credentials” in left menu -> “+ Create Credentials” in center -> “API key” should show in dropdown.
Here is a screenshot: