First, GoogleAPI traffic is perfectly safe, legitimate, and official. In this context, the GoogleAPI referral simply states that Google is grabbing your content, recommending it somewhere, and a visitor has clicked on that card.
This can be found on various pieces of Google software and even hardware. Most traffic is probably coming from the Article For You or Content Suggestion on the Google Chrome Apps and Browsers (prevalent on Android Devices).
For those who use the Google Search App or Google Voice assistant, clicks on you recommended content would also show as a GoogleAPI referral.
On various hardware pieces, like the Nest Hub, will show content if you voice search (and/or as recommendations, depending on the configuration):
The key uniting factor here is that referral traffic from GoogleAPI (referral source “googleapis”) is being recommended to the visitor in the form of a card.
If you're just noticing this referral type/domain and getting a bit apprehensive, don't worry. It's legit traffic, and relatively new to the Google ecosystem.
If you're familiar with the Google Search Console, Discover traffic would display as a referral with the googleapis source.
We hope that this clarified what the googleapis referral is!