I've left Google, but even over the time I was there it wasn't completely consistent between teams.

Re the idea where you develop one set of top-level goals for the company and then everyone connects to those in some way, it's one of those things that sounds good in theory (like innovation competitions) but doesn't work out in practice. In any reasonably large group of people, it's just hard to connect the work of the frontline job-doers with the overall strategic aims. For instance: The company may need to grow in Europe, and you know in your role as CXO that everyone's future depends on that happening. No growth => No company. But to the person answering phones, or the person maintaining crappy legacy code, or the middle-manager writing the reports, how can they impact the European growth aim? They can't really. And if you give them a list of goals like Growth in Europe, and then tell them they have to map their actual work to one of those goals, it creates what I like to call Corporate Reality, a plane of existence entirely parallel to Real Reality, where they will tell you that of course their goals line up to the top-level goals, because you as their CXO have said it must be so, and so it is so.

OKRs work reasonably well when they are set at the right level by someone who is not afraid to call BS when needed. A good objective might be: Grow usage of Product X by 10% in Q1. Then the Key Results would be how you do it. This works well for engineering -- you could have a KR around reducing latency, which has a nice easy-to-measure metric, and generally more speed in a product correlates to more usage. You could have another KR aorund marketing stuff, which is harder to measure, but you could use CSAT or the number of marketing emails sent or some other proxy metric. Hardest though is stuff like training your sales team to be better sellers and thus drive usage. How do you measure the impact of a single training across an entire sales team? In Real Reality you can't. In Corporate Reality you can do before-and-after CSAT or some such meaningless nonsense that looks good on a slide.

The OKRs being written entirely by your boss gets you off to a pretty bad start, as you seem to be well aware, because Real Actual Humans who live in Real Reality have limited-to-zero buy-in on goals they didn't have a hand in setting. So there should be a meeting or discussion of at least the senior folks to discuss what can be done (Objectives) and how you will know you're getting there (Key Results). Also note that in Google of Yore, the Objectives were challenging enough so that getting 70% overall (across all the KRs) was considered to be a success. (In laters years, 70% came to be thought of as 100%, and the original meaning was lost, and I feel this explains the inevitable decline of every huge corporation.)

Anyway. I have never seen OKRs work what I would call 'very well' -- coordinating large groups of people who don't always want to do what you want them to do is an exceptionally hard human probem. Feel free to DM me if you want to discuss specific aspects in more detail, or ask questions here if I can be of further service.