The contrast in this scene is very high, and the subject is in the shade.
So you have to lift the shadows considerably, and this will inevitably lead to noise, even at ISO 400.
The reason is that shadow pixels have much lower quality than midtone and highlight pixels, and this low quality is revealed when you brighten the shadows.
See this article for a detailed explanation: https://perberntsen.com/misc/technical/exposing.php
The noise is also enhanced by a number of your edits:
Positive Texture and Clarity values
A high Sharpening radius. You had it set to 2, I reduced it to 0.5.
Sharpening masking will protect flat areas (where noise is most visible) from sharpening. You had it set to 0, I used 90. (hold down the Option key when dragging the slider, and you'll see the effect. White Black areas are protected from sharpening, white areas will be sharpened)
You had Color set to 7 under Manual noise reduction, I increased it to 30, which removed the color noise.
Many of the Develop settings you have used are created on import because Nikon mirrorless cameras write camera settings to XMP which LrC understands and honors. I use a Nikon Z7 myself, and find these settings useless.
To stop this from happening, either zero out all settings in the camera, or create a Develop preset that is automatically applied on import.
You can either create your own preset with the sliders set the way you want them, or just use Adobe default.
See https://helpx.adobe.com/lightroom-classic/help/raw-defaults.html
You can download my version of the image here: https://per-berntsen.filemail.com/d/sfztbrbsbextqfh
It is still has a bit of luminance noise that you can remove with DeNoise or manual noise reduction.
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