While exploring our new fractal plugin for Unreal Engine 5 (OUT SOON) we've rendered 4k stills without any denoiser and with 64 AA samples but the quality is similar when rendered in real time.
No geometry was used, except for the girl. The environment is calculated at render time and the fractal parameters can be tweaked with a real-time feedback.
More info here: www.machina-infinitum.com/unrealengine