How to make all developer heroes?

As a CTO, I try to reduce "bus factor" and the "hero developer" problems.
Why these are problems? Because to scale the team, knowledge needs to be scaled too.
Scaling technical knowledge enable newcomers onboarding, deeper collaboration, and better quality development.

So what stopped us to spread this knowledge?
Well, in a pre-product market fit startup with a fast ever-changing environment
the short-term cost of writing documentation is high.

How did you tackle this problem? Or how did you see it tackled?

Also, I bootstrapped a solution below, tell me your thoughts.
https://aurel.unstack.website/beta