Apart from native support for text shortcuts, how can I enable autocomplete on Mac, presumably Cocoa applications? I mean autocomplete from dictionary or words previously used. Something like Samsung's input system has.
The closest things I've found to what you are looking for are this text editor experiment that you have to compile yourself
And this Chrome extension for Gmail https://complete.li
Both would require you to type in their respective places and then paste into your application of choice, but I haven't found anything that works systemwide.