It seems that this is a security issue that requires a command-line upgrade, but I’m seeing a forced rebuild on only a couple of the sites that I’ve checked, and those seem really old.
You have to update docker_manager first in order to see it. After you update the docker_manager, the next request to /admin/upgrade will show the message.
This might explain something I saw: I did the docker update, navigated successfully back to the versions tab and then did the discourse update. All in browser and all apparently successful. But opening a new processes tab in another window showed me the static page telling me I needed to rebuild.
In a sense, I didn’t need to - and I haven’t. My discourse thinks it is fully updated. Is it? If it isn’t, what state is it in?