Why do you want to output the writer field with kt()? But this is an issue with the underlying library (prosemirror), I think, even if you donβt use kt().
You would need something that manipulates a chunk of html. This will probably do it:
Or you could make a little custom field method that leans on some of Kirbies built in string helpers, like replace. You should be able to find the P tags and replace them with nothing using that.