Sorry for the late response but I think I have an idea what's wrong. Thing is, Renpy won't even allow this to work even without the kinetic text tag. I tested it myself and the outline still wouldn't appear. I believe the problem is that for the style {=} tag, renpy will only apply certain properties of the specified style. And sadly, outlines is not one of them. https://www.renpy.org/doc/html/text.html#style-text-tags
That said, there is an outlinescolor text tag. https://www.renpy.org/doc/html/text.html#text-tag-outlinecolor But I believe this would require the text to already have an outline, which you'd probably have to specify in your say screen. Maybe make a transparent outline that you can then replace with outlinecolor? I haven't tested this but I believe the solution is beyond the scope of my text tags sadly. But hope you're able to get your thing working!