This page of the Halo Infinite guide contains a walkthrough of the 11th main mission - Nexus. The following walkthrough explains how to win the fights at the tower, how to deliver power seeds and how to unlock the grav lift to the Command Spire.
Locate the Nexus
While completing this task, you will frequently engage in fights. The first group of enemies will appear in the first hall already. You should recognize the enemies; however, be prepared for the return of the flying machines. Kill them with some solid long-range weapons or by pulling yourself to them when they get close enough.
Also, be wary of the stationary turret. As a reminder, once you've killed the shooter, you can pull out this tremendously strong turret to use it yourself.
Use the switch to open the door and prepare to fight Hunters. These elite enemies are best attacked from a very long distance. After they get close, start running around the room and look for opportunities for further attacks. Also, look for good weapons in the area to deal more damage (heavy weapons will not work because Master Chief moves slowly with them).
After the battle, reach the terminal. Using it will uncover a hole in the floor, into which you can safely jump and slide down.
Finally, you will reach the location where you will meet first Sentinels - the flying machines. They are prone to accurate fire from a distance (in the area you'll find a good weapon shooting purple beams). It is not recommended to pull yourself to them because there are lots of machines flying over the abyss.
You must activate the gondola and defend yourself against the machines during the journey. You can make the journey easier by setting up drop walls. Destroy the machines closest to you first.
Deploy the Weapon
After the ride, go to the new marked door. You'll get to hall with spires holograms. Approach the device to access Nexus. You'll watch the cutscene and learn the next mission objective.
Enable the Grav-lift
The new task is to power 3 crucibles through finding and delivering 3 power seeds. You can reach them in any order. For this purpose, you must examine the rooms and corridors behind the doors to the left, to the right and to the right of the starting point. Of course, expect that while pursuing each seed, you will have to defeat some enemies and flying machines.
Obtaining one of the seeds involves an additional difficulty; after removing the seed from the slot, the bridge which was powered by the seed will be deactivated. Fortunately, this is not a difficult puzzle - just jump over the gap using your grappleshot.
After delivering all the seeds and watching the cutscene, go to the activated grav lift. It will transport get you to the location of the next main mission Command Spire.