Edit: Some clarification on the "secret ending"

What is the secret ending

During final mission, wait for 5 minutes at certain dialogue choice, Johnny will propose you to solo storm Arasaka tower, without taking any allies.

What's the appeal of the secret ending

It seems to make the enemies more challenging during the mission. Which makes the solo run feels more heroic. If you have an OP LV 50 build, what's better way to showcase it than walking up to the front door of Arasaka gun blazing?

Adding to the challenge is that you won't be able to save during the mission. If you die, it goes straight to the "bad" suicide ending. It keeps an auto save at the beginning of the combat though, so you can keep retrying.

According to u/d07RiV there's more interesting mechanics: Should also mention that the final mission is essentially timed, because your max health keeps going down over time (or rather you'll be capped at 90%, 80%, 70% etc of your max HP if you take too long). You have to try really hard not to make it, but you'll have a bit less HP to work with.

If you don't like the regular endings especially how they deal with certain characters, this is the way to not have them involved.

At which point should I wait 5 minutes

I know almost all the guides say you should wait after picking "You and Rogue should go", which implies you need to finish Rogue's side mission.

That is NOT true. I waited at the choice of who to go in with (Arasaka, Nomads or Rogue, if you've done corresponding side missions), 5 minutes without making a choice, Johnny offered me the solo run.

First of all, the actual trigger of the secret ending

The 70% relationship with Johnny is NOT the trigger. The only thing that matters is the dialogue choice during Chippin In:

• “[Inscribe Johnny’s Initials] Let’s do something about that.”
• “The Guy who Saved My Life” –> this seems to be the first actual trigger for the secret ending, VERY IMPORTANT
• “Nah, fucked that up too” –> this seems to be the second actual trigger for the secret ending that is mandatory
• “What do you want from me?”
• “OK. But as second chances go, this is your last.”
• “You were a real dick in the beginning”
• “When you said you let down your friends…”
• “Smasher biz really got to her.”
• “Yeah, I’ll call Rogue.”

From <https://www.powerpyx.com/cyberpunk-2077-chippin-in-walkthrough/>

Myself, among many others, has gotten to the secret ending without having 70% relationship with Johnny.

Then how to check if you've made the right dialogue choices

Install Cyber Engine Tweaks at Cyberpunk 2077 Nexus - Mods and community

Open up the console and type command:

Game.CheckFactValue("sq032_johnny_friend") 

Result "1" means you made the correct dialogue choices, "0" means no, you won't be able to trigger the secret ending. This value changes right after the Chippin In final dialogue.

Finally, how to get the secret ending if you missed the correct dialogue choices (or don't bother to do Chppin In for whatever reason)

Open up the Cyber Engine Tweaks console, type command:

Game.SetDebugFact("sq032_johnny_friend", 1)