The bounce is invisible from the outside -- an event horizon means causal decoupling. From outside, the formation of the black hole looks like the good old "frozen star" picture.

There will never be observational evidence on what happens on the other side of any event horizon, you'd have to cross over to the other side to see it for yourself (but you won't be able to report back your findings). There's a fun greg egan short story about that ;)

What's the story?

"The Planck dive", freely available on Greg Egan's website https://www.gregegan.net/PLANCK/Complete/Planck.html