The OKRs for an internal product in a company are very different from customer facing products from a product management stand point.
The reason being, the goals for external products are starkly different from that of internal products.
Take a collaboration tool in a company for example. Many would assume that the KPI for a collaboration tool would be its adoption among users which can be measured through number of accounts created, number of logins, active users, average session times etc.
But if we look more carefully, these KPIs may not always serve the objective of maximizing the benefits for an internal tool, which in most cases would be to increase productivity within an organization.
Since productivity is tied directly to how much time employees are able to save while solving critical problems, the tool will be effective only if it serves as a platform for people to hop on it and collaborate to solve a problem.
But that's not something we can easily measure as a product KPI.
The only way to know if the tool has played a part in decreasing average time spent on critical issues, or increased developer velocity is by carrying out user interviews or surveys within the organization.