How do you identify the highest impact projects on a platform team?
Impact is typically measured by customer and business value that product/project brings in. First step is to understand customer scenarios/workflows and associated pain-points and needs. Combine that with business opportunity of that investment, also having a close eye on the market and compete landscape. Finally, use rigorous prioritization to focus on highest ROI - take into account both customer/business value as well as associated cost to deliver. This is no different from a typical Product team. A key focus on platform team should be to invest in durable, long-lasting capabilities that will benefit many customer as opposed to focusing on short-term wins for a select set of customers (this can result in custom solutions that become hard to generalize in future).
First, I start with defining the impact. In some cases, the business could benefit from cost savings, better SLAs, or faster time to market for new products and features. It all depends on the business and market conditions, so aligning with your executive team is the first thing I'd do.
Next, I focus on capturing, analyzing, and synthesizing qualitative and quantitative data inputs. Personally, I like to meet key stakeholders (PM/EM leads who lead other pillars) to understand their pain points and needs better.
With these inputs, I usually generate two artifacts: (I) a platform strategy document outlining how the work we do aligns with business and market signals (II) a shared backlog among teams with RICE scores to help calibrate priority among different types of initiatives.