Adjust auto close hours for Discourse post topics
TL;DR: go into settings for a specific topic, and set Auto close hours.
I am administering a Discourse forum where old posts were getting automatically closed after 30 days. I could not find out where these settings were hidden. In the forum settings I was searching for a diversity of settings by keyword without any luck: old, cold, auto, close, lock, 30.
Eventually, skimming through the logs, I could see that during setup, another admin had set these settings on a per-topic basis. So this is in fact a setting applied to individual topics, not to the forum globally. I guess it makes sense when I see it now, it was just so hard for me to find.