Destiny 2 players probably expected Trials of Osiris to happen on August 27, 2021, again but this will not be the case as the activity won't pop up for a while.
Trials of Osiris used to start at reset every Friday before Season 15 of Destiny 2 but there will be some major changes coming to the activity now, including the times at which it's available.
For starters, you will not be able to play Trials on August 27 or September 3, 2021. The game mode will only return on September 10 as the devs are preparing to introduce numerous changes that should make it better for everyone around.
On top of that, Bungie announced several occasions where Trials outages will be happening in the future. The first week of every season will be devoid of Trials from now on as Bungie wants people to farm and explore the new stuff.
Similarly, there will be no trials before the World's First race in any new raids so the teams can focus on preparing for it without having to worry about missing out on Saint's game mode.
Iron Banner will no longer clash with Trials for the player pool either as Bungie concluded having both of them running at the same time is damaging to both activities, which probably also means that the player base is simply not big enough to produce somewhat decent matchmaking in two big PvP activities simultaneously.