It seems to have reset, but I find it’s actually much better than before after some intervention/training when I first updated.

Autocomplete got worse because the new system in iOS17 didn’t retain training data from prior versions. It reset everyone back to untrained. I’ve been manually correcting specialized language I use daily (e.g. “iRacing”) on my 12 (non-pro) since iOS17 release, and now it gets it correct 99.5% of the time.

So, rather than turning it off, manually correct the incorrect completions and use the suggested words bar frequently and it will learn how you type. It’s just having to start over after tossing out several OSes worth of training that makes it feel worse.