OKRs are designed to exist in levels, “trickling down” in a way that narrows them down more and more as they reach specific teams and individuals[0].
A goal such as “Increase customer retention” could be a legitimate higher-level objective. From key results on that objective, we get objectives for specific teams working on various aspects of the product.
(For example, “Reduce churn rate by X” likely isn’t going to be just about engineering; copywriters and others may be involved. Down the line at some point there may be an engineer’s personal key result such as “launch customer feedback collection system by X date”, or something else specific to circumstances.)
I believe that wholeheartedly adopting OKRs in this multi-level fashion is helpful even to companies with a just a few employees, and how objectives and results are translated across levels is a good measure of management health overall.
[0] Rick Klau talks about it in “How Google set goals” https://youtu.be/mJB83EZtAjc?t=1951 (2013)