After the credits

[AltesBlank]

So i beat the game 10 times and got a nice song for it, but what now i read that i have to do 10 more runs to unlock endgame but what does it add and is there still another boss?
Pls keep it vague i dont wanna spoil myself

[Wintermute]

There's a story epilogue, and there's "extreme measures 4" which you probably didn't unlock yet. There's no real edngame to unlock otherwise.

[chris.ferrantegerard]

You've finished the regular ending (10 full clears). There's a short epilogue but it will take you far, far more runs to get, it's pretty grindy. The Pact of Punishment has Extreme Measures pact to make harder, alternate versions of boss fights. Otherwise you can keep farming higher levels of heat for challenge.

[El Goretto]

As stated earlier, it's more narrative "side quests" (Fated list related) that keeps the story going on, than an alternate or "real" ending.
But turning on features on the Pact of Punishment greatly improves variety in fights (bosses of course, but elites too). Don't forget weapons aspects (just unlocked spear secret aspect, it's awesome...).