I track product usage out of the gate and usually shoot for 30% attach rate (adoption) within the target audience I'm serving.
From there I look to our company North Stars: win rate, deal velocity, pipe gen, expansion rev to inform PMM peformance.
But product activation and engagement/reactivation is super critical to initial launch measurement and performance.
There are two categories of KPIs - business KPIs and launch performance KPIs. For both types, the KPIs you choose to track depend on the goals of your product launch.
Let's say you're introducing a new revenue-generating product. The main business goals of the launch might be to create brand awareness for your company and create $XX pipeline for your new product, and close $XX ARR within two quarters (depends on your sales cycle).
Increasing brand awareness
Create pipeline for the new product
The main takeaway is that your business and launch performance KPIs should go hand in hand; the most important thing to do as a PMM is to frame your goals in terms of business outcome. Think about the goals you want to hit as it relates to product adoption, pipeline, revenue, etc. Too often, PMMs can get stuck in measuring only the launch KPIs, because that's those are easier to measure. But, it's important to identify those business KPIs even if you can't immediately measure them -- it ensures that you're tying your launch to business objectives, highlights the need for better visibility & tooling that you can build in the future.