If Discovery was ending this Season, the series would still be airing on Netflix. Paramount/viacom/cbs wouldn't have forked out money to pay out the contract with Netflix if they intended on cancelling the show. The whole reason the deal fell apart was because Netflix wanted another multi-season contract, which obviously didn't jive with the plans for Paramount +. There is also the recent interview with Bob Bakish the head of viacom, indicating that he was pretty pleased with the amount of new subscriptions Discovery brought with it in november.
My guess is the delay on announcing season 5 has something to do with the end of the netflix deal.