After having published an update for the Crimson Days event in Destiny 2, Bungee had to put the servers offline.
They are back, but people encounter problems trying to connect.

Destiny 2 is temporarily with full capacity

Unfortunately, there are so many people who try to enter Destiny 2 at the moment that the servers are under pressure.
However, you had to expect it.

Almost the entire active population of Destiny 2 is trying to connect at the moment.
When Bungee was forced to put the servers offline, it meant that everyone playing the game had the start, then now, the whole active population is trying to come back for Crimson Days and weekly reset.
It is a lot of people who are currently bombing the connection servers.
As such, if you encounter connection problems, the best thing to do is show a little patience.
Unfortunately, these problems have become fairly common since Destiny 2 moved to Steam.
All you can do is sit down and wait until you are treated in the queue.
I would not advise trying again, because you will lose your current place in the queue and all the people behind you can move on a step forward.
Stay patient.
The moon will always be haunted in a few minutes when you finally enter the game.