X1C works fine completely offline now[1], however it still has a stupid restriction where their slicer can't find the printer if its on a different subnet unless you generate the announcement packet yourself.

[1] it was much worse a few months ago, but an incident where a cloud outage resulted in a lot of damaged printers (when jobs were erroneously resent after they completed without a re-leveling) seems to have motivated fixing many of the remaining gaps with local operation.