Early this year I had a f* 3 hrs conversation with an Apple support, btw, 3 persons... I've report this issue on Reddit, Feedback app and through Apple's site, they were awere about this problem, but they done nothing to fix it.
In this 3 hours conversation I factory reset my phone then the problem stopped for about 2/3 days, them it come back.. If I remember correctly, they said that iOS 17.3 would fix this.
My first language it's BR-Portuguese and the predictive text its INSANE! It change the words all the time to words that aren't even close to what I'm trying to write.
Idk why Apple downgrade their keyboard so much.
I've test in an iPhone 6 and an 7+ with iOS 15.8 and the typing experience it's another level, very good predictions and no lag.
I wish they fix this.