You could do this outside of Discourse with webhooks. I’d recommend a platform like n8n or Airtable to receive the webhooks, then create an automation to send an API request to close the topic at a time interval of your choosing (eg a relative time of 30 days).
We don’t close topics like this, but we do many other automations outside of Discouse similar to this, and we get around these limitations often by sending webhooks out and API calls back in.