You might ask, if each sprint ends up with an incomplete work, when can we see a stable product  ?

Answer is the work around invented by the thought leaders. It is called Stabilization sprints.

What are stabilization Sprints ?

These are sprints dedicated towards tasks such as

Defect fixing
Fixing technical debts
Completing any final rounds of testing
Update or fix any architectural issues
Getting ready for the release by completing release notes, etc

Stabilization sprints can be scheduled based on the need of the hour. There is no hard and fast rule around when it should be scheduled.

Many people call stabilization sprints with different names based on the specific activity being executed. Some names are, Testing Sprint, Technical Debt sprint, Analysis Sprint, etc