So, I have completed all the achievements of the game, however the last one, "Never Fade Away", does not appear in my account. And the general section 'Achievements' have stayed at 98%, What can I do?,

Wait - sometimes it takes time to reflect achievement. Restarting GOG and restarting game sometimes speed it up.

If that does not help - replay the finish from earlier save before deciding dialog.

Also, congrats on 100%. I still have melee fighter build with nomad ending to try out .

Got the same issue, I'm also stuck at 98% even though the notifications say I've unlocked 100 % of the achievements. Very frustrating, there seems to be no solution so far. I've restarted launcher and game numerous times, nothing works.

Never Fade Away is an achievement exclusive for PlayStation. If you are in PC, you must now deal with impossibility to accomplish 100%. I'm still trying to deal with my OCD, doing my third playthrough... xD

I'm still checking GOG few times a day to see it if somehow fixed itself :D