I've decided to put my PC out of its box and install in on the wall.
Advantages: no more dust stuck in the PC box and dust fly away immediately from the wall mount thanks to the various fans that are installed.
The components here will allow you to install the ATX power supply, the HDDs, a graphical card (an AMD Radeon R9 390X) on a wooden board.

The fan on the right side of the HDDs is a 120 x 120 mm fan.
To deport the graphic card you'll need a PCI-e X16 Riser Cable.
To assemble the GPU support you'll one 5x30 mm screw
I covered my wooden board with a "carbon like" sticker.

The caddies are for 3.5" HDD. Assembly is done with 3x15 mm screws
For the upper HDD you need to print: 1x HDD holder - top left.stl + 1x HDD holder - top right.stl
For all the HDD in the middle position you have to print : HDD holder - mid left.stl + HDD holder - mid right.stl (you can stack as many HDD as you want)
For the lower HDD you need to print: 1x HDD holder - bottom left.stl + HDD holder - bottom right.stl

Print 6x Motherboard support.stl to hold your motherboard in position. You'll need 6x screws of 3.5 x 19 mm. One of the photo shows the printing orientation on the heat bed to avoid support.

The "kill switch" for the power on and the reset are available here: https://www.thingiverse.com/thing:4313332

Update 03/12/2021:
I've replaced my motherboard by a longer and larger one (Asus TUF Z390-Plus) and as the motherboard's support that I've designed are movable, no problem at all.

I've also created a personnalised I/O shield plate for this new motheboard.

Geeetech Prusa i3 Pro B