Android's Gboard always suggests replies in chat apps that fit the context of what my contacts write.
If my previous message had been related, I would assume it predicted what my contact would say in response and make a suggestion based on that. But even if the contact changes the topic, the suggestions are appropriate.
I don't expect that the apps all share the conversation with Gboard. So how are the predictions made.
It seems unlikely that it would take screenshots and base predictions on that. But otherwise I don't know how it is possible.
I haven’t found something that has good support for swiping words. Anysoft Keyboard gets too many words wrong.
If I thought Google was actually collecting what I type, I would put up with typing manually on another keyboard. But that kind of data collection without consent is illegal in the EU. I’d put the risk of Google breaking the law here at less than 10%, which is tolerable.