The UK's departure 6 months ago is a milestone that's more political than actual. During the transitional period of the withdrawal agreement, the UK is effectively a non-voting member this year as it has no option to opt of EU regulations or budget contributions until the end of this period. Other parts of their departure, like the Northern Ireland backstop have their own conditions before the UK can adjust them.

Describing the departure as in progress rather than done is very much accurate.