Britbox stopped taking new subscriptions when ITVX launched - winding down in UK so not really worth promoting.
BritBox promo channel is no longer on the epg, was on 331. Netflix,Amazon and BT Preview are still there.
The BT statement on the BT TV web page today reads
As of the 1st June 2023, BritBox on BT TV will no longer be available to new customers. Existing customers will continue to have access to BritBox on BT TV as usual