This may sound like an advert, but it's not - I used "Backuptrans Android WhatsApp to iPhone Transfer for Mac" last year when I moved from Android to iPhone, and surprisingly it actually worked!

I could export all my Android (Nougat) messages and media, and restore it onto my iPhone (iOS 11).

It was a bit dodgy though - it asked me to install an old (custom?) APK first to export my messages, and the iPhone restore process looked like an actual iOS system restore..