China may seem like another planet, but it’s actually part of Earth.

When the question is “How do we fix this global environmental issue?” (which is part of solarpunk even if not all of it), you literally cannot just move county.

The "solarpunk" ideology seems to include things like decentralization, local governance, and anti-authoritarianism. In this respect, China seems like an ill fit.

Decentralization and local governance aren't foreign things for China. It has a remarkable amount of authority on a local level (at least provincial). You can also google ratings based on share of subnational public expenditure in total public expenditure, China is the top.