@baldur I occasionally have to use Google Docs for work (I'm a writer), and I've been slowly tracking its spelling checker's increasing inability to recognise grammatically correct but either unconventional, old fashioned or extremely formal constructions in British English.
As others have noted for other languages, some of its suggestions are very obviously the result of bring trained on bulk material including errors and lacking many examples of the kind of phrasing it fails to recognise as correct.
Meanwhile, LibreOffice Writer and this ancient copy of Wordperfect for Unix I use do just fine.