This is a hard one as I am sure there are a ton of layers to unpack here. Whenever there is a question around metrics, I would first look to the customer and understand what customer pain points your product area is solving for. Then see how those needs and your business goals align, and how your specific area can help solve for that. If it is a matter of stakeholder management that is a different story, but engineering, product and design should really have shared KPIs.
Get into a rhythm by understanding the business/company goals. Then understand how the tech works (look at the customer/user interface first and then make sure you understand how the system behind the UI works). Begin collecting data in a transparent way and share your learnings with your stakeholders and leadership.
Conduct user research (both qualitative and quantitative) to help illustrate what product areas (epics/themes) you want to focus on and how these connect back to the business/company goals.
The worst KPIs to commit to are the ones you can’t commit to at all. We can set targets and metrics and make dashboards, but that’s exactly what they are - targets. I recommend looking at past performance and trends within the data and setting a realistic yet aspirational target to work towards. After that, begin iterating on your target. Revisit the KPI, analyze, adjust, and communicate your findings.