Hi, and welcome!
Please see the FAQ: What's a reproducible example (`reprex`) and how do I do one? Using a reprex, complete with representative data will attract quicker and more answers. It's much easier to cut and paste a single block.
If @Abderrahim's suggestion of an alternative toolkit is an obstacle, you may (haven't checked it) be able to correct by taking all_numeric() from step_knnimpute and using it as an argument to recipe
recipe(Ozone ~ all_numeric() ... )
This is untested by me, just something suggested by the documentation for all_numeric