Mac OS has a not very well-known, but nonetheless pretty useful feature built in, namely word completion. The feature is showcased in well in part two of this video and further explained here.
As far as I understand it, it seems to be a feature only available to Mac apps that use a cocoa text system. Which is probably why you cannot use that feature in Drafts. But seeing as Drafts is so well integrated with the functionalities of Mac OS, would it maybe be possible to somehow enable the word completion Drafts for Mac, too?