This motherboard cover is designed around fitting a Noctua NF-A9x14 in to my CR6 without raisers or changing the outer shape.
This should accomodate any 92mm fan 14mm thick, and presumably also fans 15mm thick (untested) - if it doesn't conflict with the mount for the buck converter.

There are 4 variations, countersunk or flat, and self tapping or inserts. The flat variations still have countersinking for the 4 fan screw holes. The pictures I've added are for the countersunk with inserts variation,

To install a 12V fan in the CR6 you will need to use a DC-DC step down/buck converter, as the CR6 fan headers provide 24V. This cover includes a bracket to mount the commonly found converters with M2.5 screws, using the insert or self tapping variations.
I found it easiest to cut up the spare adapter that came with the fan, and solder (& glue) this to the converter to make un/install easier.

Recommended parts

• 2x Countersunk M3*6 screws
• 1x Countersunk M3*12 screws
  for mounting buck converter:
• 2x M2.5*4*3.5 brass inserts
• 2x M2.5*6 screws

I found this printed fine without supports using layer height of 0.2mm or less. Wall count can be important to set appropriately. Good dimensional accuracy settings are likely important.

I would suggest a variation of PLA over PETG, as I found my PETG prints to be too flexible.

Original design, but insprired by https://www.thingiverse.com/thing:4716529