1.) Any hints where to find up to date binaries for a aspell, or hunspell e.g. any of the supported spell checkers?

I did only find very old precompiled binaries and nothing "official".

2.) Windows spell check API

Windows 8 onwards has an integrated spell checker API.

More info is available here:

https://docs.microsoft.com/en-us/windows/desktop/Intl/about-the-spell-checker-api

What would be the best solution to integrate this into flyspell?

Is it possible to call COM from lisp code?

With kind regards

Thomas