You literally cannot obtain the Izanagi's Burden sniper rifle in Destiny 2 right now.
Izanagi's Burden has perhaps the most obnoxiously long quest in Destiny 2. First, you gotta find the Mysterious Box in the Black Armory. Then, you gotta forge three keys by completing all three forges and then get the fourth key from Ada-1 by going to the Leviathan and killing a bunch more dudes. Then you gotta do public events, strikes, kill more things, and THEN turn in a rare bounty. They don't call them "rare" bounties for nothing.
If you do all of that, then you have to do a pair of tough dungeons before finally killing a boss in the EDZ. And we gotta stress how horrifically condensed this whole process is. You can find 20-minute-long videos on YouTube explaining the process and they still leave details out.
Anyway, it doesn't really matter. With the current bugs plaguing the Black Armory's forges, getting Izanagi's Burden is essentially impossible.
That sad analysis comes courtesy of Reddit user LeonZ50, who points out that the Forges are still broken, causing crashes and other issues that prevent the rewards from triggering. If that happens, you could wait up to 3 days for the correct forge to come back into the rotation.
Even if the forges weren't broken, Ada-1 is afflicted with a bug that prevents the Key Mold from being given unless you have the Rekindle the Flames quest. And on top of that, rare bounties are still hella rare, so even if you progressed to the step where you have to turn in a rare bounty, it would take quite some time
The top commenter says they were able to complete the quest in a month with everything working as intended. With the current bugs, it's just impossible to get Izanagi's Burden.
If you’re looking for a good sniper rifle in Destiny 2, steer clear of Izanagi. You’ll just give yourself a huge headache for trying to get this rifle.