Google seems to be testing a new option for the Book Online call to action option that does not use an online booking service but rather lets you call the business directly. The button says “call business” and then will dial the business from your mobile phone.
This was spotted by Colan Nielsen who shared this screenshot of this feature on X:
Keep in mind that these local listings already do have a call button and the phone number listing on their Google Business Profile listings.
I am not sure how this differs?
Forum discussion at X.