Is there any “fastscroll” library for LazyLists and/or LazyGrid out there? Haven’t found anything. Or Can me someone point how it could be implemented?

What do you mean by “fastscroll”?

I see. Not that I know of, but shouldn’t be very difficult to implement.

the ListState isn’t the issue. It more like where do I get the values / headers from. should I group the items myself or does the dev need to put in a map so I can generate the scroll items?

That’s an API design decision… You could have the developer provide the mapping from letters to indices, or write a function that takes a list of strings and creates such a mapping, or both.