The Monolyth is easily accessible. The 3 Glyphs are on top of the pillars.
One pillar can be easily climbed on. From there you can scan Glyph 1 & 2.
From there you can jump on the pointy center pillar to scan Glyph 3 or you can use a console on ground floor to activate Remnant pillars. With those you can access Glyph 3 easier.
Monolyth activates after using the console. No Decryption needed.
Remnant Pillar Console
There are 4 Consoles here at ground level. 3 consoles activate the remnant pillars to climb to the Glyphs.
Glyph 1 is the pillar to the left that can be accessed with the lower remnant pillars.
From the Glyph 1 location, you can scan Glyph 2.
For Glyph 3 you have to find the setting with all 3 consoles that form stairs up to the pillar.
Monolyth activates after console interaction. No decryption necessary.
Pillar Stairs to Glyph 3
After activating the power on the top console, you'll see 5 consoles in front of the door.
All 5 lights need to point to the door for it to open.
This is what the consoles do:
#1: 1 & 2 are going up while 5 is going down and vice versa.
#2: 1 & 2 & 3 are going up or down together
#3: 1 & 2 & 3 are going up, 4 is going down and vice versa.
#4: 3 & 4 are going up while 5 is going down and vice versa
#5: 5 is going up, 1 & 4 are going down and vice versa
Go through the door and continue until you get to a big wide open room. There is a treasure chest behind a force field here.
There are two consoles to the right. Activate them and jump on the pillars that just appeared to activate the consoles on the high pillars.
Then go back and use the two pillars again so all the 4 lights point to the center. Now jump to the center and use this new console. The door in the far back opens.
Go through the door and use the console at the end of the corridor.
Go all the way back to the wide open room. We're now going to the opposite side.
Jump down to get to a console. Use it to activate the remnant bridge.
Go all the way up past the bubbles and open the door to get to a room full of consoles.
Solve the Decryption at the console at the top of the pillars.
Now the consoles on the floor. Always use the one that doesn't have a light. Otherwise everything resets.
Go to the console at the door and activate it. The shield is now deactivated.
Now go back to where the energy bubbles are. There is a console that opens a bridge to the lockdown console at the far end of this area. Use it and go back to the center to cross the bridge and deactivate the lockdown.