You will need low intelligence to unlock this achievement.
I started the game with a high intelligence stat, so I assumed I’d need to create a new save and replay to unlock it.

Later, I found out that wasn’t necessary. I reloaded an older save to test.
You can use Adrena-Time to reduce high intelligence enough to enable the Dumb dialogue option required for the achievement.
(Consume one at a time (max stack of 3) and wait 15 seconds before using the next if needed. You can track the effect by checking your character stats.)

Then, my partner discovered that you don’t actually need to lower your intelligence that much. You CAN unlock it with +3 intelligence, but first, you need to get the Permanent Concussion flaw. This can be obtained by shooting or hitting exploding barrels after each cooldown, or by stepping on mines.

(Note: On easy or medium difficulty, you can only have up to 3 flaws, but on hard or supernova, you can accumulate more.)

Here is a step-by-step guide:

Reach the Hope Bridge terminal during the main storyline quest Kept Secret But Not Forgotten.

With your intelligence lower than before. Check in the Character Summary screen in the menu.

Interact with the terminal.
Follow the dialogue choices:

- Comms
Patch Ada through
-I'm ready to skip the Hope
-Skip the Hope to Terra 2
-I'm skipping it myself
-Stand back, ADA. I know numbers real good

(Note: If your dialogue options are different, check again to ensure your intelligence is Below Average, and try again)

• Unlock achievement by starting and finishing the game on Supernova difficulty
  
• No difficulty lowering allowed.
  
• Save allowed manually and only on your ship.
  
• Bring companions like SAM and Nyoka for skill boosts; 60+ Inspiration helps.
  
• Explore before boss fight to find 3-piece password to disable RAM.
  
• Respec at Unreliable to boost skills if needed.
  
• Complete the game on Supernova difficulty; the Hard and Any Difficulty achievements will unlock too.

Final boss options:

-Use high Persuade (100) and Science (85+) to skip fight via dialogue.

-Hack terminal near boss room entrance to disable him (100 Hack/Lockpick/Science required).

-Fight boss directly (level 30–36, manageable if well-leveled).

-Use Holographic Shroud + 60+ Dialogue skills to sneak and dialog-check areas multiple times.

it's Spacers Choice!

First,
If you comment something like "JUsT Git Gud," I will delete your comment.

Second,
If you don’t want to grind, here is my save.
https://drive.google.com/drive/folders/1cP6ma96qbPymQcOULU6ndOY-nOJSeGEw?usp=sharing

Where to Put the Save?
Drop the file here:
C:\Users\YOURUSERNAME\Saved Games$$The Outer Worlds Spacers Choice