OKR is a goal management framework that helps companies implement strategy.
Apart from treating OKR based on its definition, it is very useful to understand OKR as...
A way of working
When a company is evaluating OKR, the leadership team is essentially on the path to adopt a new way of working.
It is like an agreed-upon convention to enable related parties understand what's expected from them. And vice versa, what they can expect from others. For example, during the OKR setup and review, I know exactly what my manager and peers expected from me, terms of my commitment (KR) and accountability (scores). Also, what I can expect from them.
OKR is a way of working that everyone understands and respectfully executes. It is not too much to say that it is the responsibility of all related individuals — not management nor HR — to oversee whether this way of working is followed and respected.
Because leadership doesn't come from a title or role. It comes from responsibility.