In Season 20 of Destiny 2, the Immortal SMG was added to the game as a powerful new weapon for players to obtain. With SMGs dominating the primary slot for many players, this new addition is highly sought after due to its Target Lock perk that is wreaking havoc in the Crucible.

Getting the immortal through Trials Of Osiris Engrams:
To get the Immortal SMG, players must participate in the Trials of Osiris, a high-end PvP activity that only runs on weekends. This mode is available starting on Friday at 1 PM EST and closes during the weekly reset on the next Tuesday (also at 1 PM EST). However, if the Iron Banner is active, the Trials of Osiris will not run during those weeks.
While players were previously required to bring a pre-made Fireteam to the Trials of Osiris, this requirement was changed during Season of the Lost to allow more players to participate. The goal is to complete seven matches without losing any, which is referred to as going Flawless, but players can still earn loot even if they lose. Players will receive reputation gains that increase based on the number of rounds they have won in Trials of Osiris matches.
As players rank up (Guardian 1, Guardian 2, etc), they will be able to claim a Trials of Osiris engram from Saint-14 in the Tower Hangar. These engrams will decode into a random piece of armour or a weapon that can only be obtained from the Trials of Osiris. If players are lucky, they will get the Immortal SMG as a random drop from one of these engrams. However, since this requires RNG, it is not the most reliable method for acquiring the weapon.
Other methods to get the Immortal SMG:
Alternatively, if players are having difficulty obtaining the Immortal SMG through RNG, they can reach Rank 10 in the Trials of Osiris reputation to claim a guaranteed Immortal from Saint-14. The other option is to go Flawless and unlock the Lighthouse, which is a unique destination where players can find a chest with a weekly rotating Adept weapon. One of these adept weapons can be the Immortal SMG. Going Flawless through random matchmaking is difficult, so it is recommended to go in with a pre-made Fireteam to increase the chance of success.
In conclusion, the Immortal SMG is a highly sought-after weapon in Destiny 2 due to its powerful Target Lock perk. To obtain this weapon, players must participate in the Trials of Osiris, a high-end PvP activity that only runs on weekends. By ranking up and claiming Trials of Osiris engrams from Saint-14, players can have a chance to obtain the Immortal SMG through RNG. Alternatively, reaching Rank 10 in the Trials of Osiris reputation or going Flawless and unlocking the Lighthouse can guarantee the Immortal SMG. It is recommended to go into the Trials of Osiris with a pre-made Fireteam to increase the chance of success in obtaining this powerful weapon.