Setting expectations first:

• I wouldn't be surprised if more than half of all engineers never get to IC6 in their entire 40-year career. There's a reason IC5 is considered a "career level" at most major companies.

• That said, 2.5 years from IC5 → IC6 is reasonably spritely, all things considered.

I don't know you personally so can't have an informed opinion about whether your appraisal of yourself (and the rush implied in your question) is reasonable given your talents and abilities, but I wanted to surface those expectations explicitly.

Managers and mentors would kept saying "create scope" but there were not a big enough problem that already an IC6 was not working on.

Is that the case? That you had multiple managers and mentors advising you to "create scope" where it was impossible? I'm trying to get a better sense the accuracy of your perception of what's blocking you from growth. If you have multiple managers and mentors advising you to do something that is impossible, you arguably have many terrible managers and mentors... or perhaps another parsimonious explanation is that they see a path where you don't.

It seems to me the best way to 6 is "influence in the org", but Meta seems much more top-down than before nowadays, so it seems people who get the opportunities on these top-down projects are the ones already having influence, so its hard to create own scope now.

I don't think this can be true. What you're saying implies that no one at Meta will grow from IC5 to IC6 because of some structural change in the company. I'm willing to bet this can't be true. There have got to be hundreds of people going from IC5 → IC6 at Meta in any given year. Perhaps especially at its current size, since large companies often succumb to grade inflation.

I fundamentally question the claim that Snap and Pinterest are faster places to grow, and that you're stuck in IC5 simply because you're at the wrong company. There are of course situations in rapid-growth companies (e.g. early Facebook) where people are given opportunities to learn much more quickly than at stagnant companies... but Snap and Pinterest aren't those fast-growth companies abounding in opportunities.

Your entire question and tone externalizes the cause of your stasis. Knowing only what you've told me, the error bars on my judgment are huge: but I'd hazard a guess that externalization might be the root explanation of why you're not growing. Everything you'd said is about how the situation isn't right for you: the team's not right, the mentors and managers are giving advice that's impossible to implement, friends are growing faster simply because they're at other companies. You haven't mentioned a single thing you'd like to grow in yourself to earn the IC6.

If I were a betting man, I'd likely guess that your best path to growth is to solicit feedback and introspect about the true blockers to your continued growth. If a single person is promoted from IC5 → IC6 within Meta, you should ask yourself how you could have been that person. And the answers need to be something within your agency; otherwise, you're just externalizing blame, and you may well find yourself growing much more slowly than your talents theoretically make possible.