If you’re asking purely about the visual style, you could go through the generated Adwaita.css (and variants for dark/hi-contrast) and pick out the styles that apply to widgets in GTK4. You would then need to include them in your application’s stylesheets.
If you are also asking about the widgets included in Adwaita, then you’re just going end up re-writing libadwaita.
Needless to say, this will be a lot of work and anyone you ask for help will probably just say “use libadwaita”. So the answer is yes, but the road ahead of you is long and lonely 