Many years ago, during the dot com crash, so not exactly by choice, I went from a startup to a government department.

I found it utterly soul destroying at first, but it was one of the best things to ever happen to me. I learned how to operate in a large organisation on much bigger and more impactful things.

It is very slow, and you may find that it really isn't for you, but I'd advise you to give it a go. There's a lot of good advice in this thread.