it is not a guide per say but a warning for this achievement
it somehow glitched on me cause apperantly i didn't go the route the game intended and didn't go for brother 2 after the side mission of the laser machine that breachs a hole for u to go through, i dont know how it didnt register for me the side quest "brother 2 underground" but it made me stuck at 96%
just make sure to tick off these side missions as they are what you need to unlock it
*****
1-Rescue Marianne
2-The Silent Outpost
3-Chemical Warfare
4-Lenz's Secret
5-Laser Breach Device
6-Stolen Research
7-Radio Propaganda
8-Claude the Armourer
9-Brother 1 Underground
10-Transmitter
11-Data Tape
12-Brother 2 Underground-----this is the damn mission that didn't register for me, just make sure to follow it exactly after the laser breach device
13-The Protohund
14-Prison Break
15-Zitadelle Schematics
16-Zeppelin Sabotage
17-Sabotage Launchers
18-Infiltrator's Report
19-Investigation Cleanup
20-Missing Resistance Fighters
21-The Robotermorder
22-Lothar and Juju's Trap
23-Missing Partner
24-Da'at Yichud Artifacts
25-Statues
*******