Blizzard have posted a list of weekly activities and rewards that will not be available until the very first reset of the expansion, 1-2 days after launch.
DF First Days Content (Source)
We’ve configured Dragonflight to prevent most weekly rewards from appearing prior to that first weekly reset. As a result, the following content will be unavailable until the new week starts:
Dragonbane Strongbox from Siege of Dragonbane Keep (Epic quality)
Grand Hunt Spoils (Uncommon, Rare, and Epic quality)
The weekly quest “Community Feast”
The “Aiding the Accord” weekly quests
The “Show Yer Mettle” weekly quest
Weekly Valdrakken professions quests of any kind
Weekly PvP quests rewarding honor
We want players to level at their own pace without feeling like they’re missing out on a week of rewards if they fail to reach level 70 within a few hours after the expansion launch.