OKRs that are all-or-nothing are fine in practice, when you have ways to measure progress.

For example the objective "Land a team on the moon" is all-or-nothing, and has progress indicators such as "Orbit a team around the moon", "Orbit a team around the earth", "Prove mission control performance during a crewed mission", and so forth. Each of those all-or-none items can have sub-OKRs, sub-KPIs, sub-metrics, etc. as you wish.