What are the potential career paths for a PMM who wants to spend more of their time doing research instead of GTM?

Because the role of PMM can vary greatly between organizations, your best bet may be to find the company where the PMM contribution is weighted more to inbound, product-development work. I've also structured teams with one or two roles that focus on inbound work across a portfolio while most of my team's energy was tied to GTM efforts. So, I think you can stay a PMM who specializes in research, insights and product development, it just may require digging a little deeper to find the right fit.

And, depending on where you are in your career journey, you might consider taking a rotation in a purer research-heavy role (e.g., Strategy, Marketing Insights, Policy) to see if its a better match for your passions.

There are specific roles that are research based, but usually tangential to PMM (aka might sit in the PMM team, might sit elsewhere)--such as competitive intel or research and insights.

But speaking frankly, the volume of PMM roles that focus on GTM likely outweigh--by some order of magnitude--the volume of PMM roles that focus on research.