According to the data sheet, the power supply may be a maximum of 155mm long if you want to use both 3.5 inch HDD slots.
However, the Be Quiet power supplies have a length of 160mm, e.g. STRAIGHT POWER 12
750W.
How many 3.5 inch HDD slots can be used with a 160mm power supply?

Question

According to the data sheet, the power supply may be a maximum of 155mm long if you want to use both 3.5 inch HDD slots.
However, the Be Quiet power supplies have a length of 160mm, e.g. STRAIGHT POWER 12
750W. 
How many 3.5 inch HDD slots can be used with a 160mm power supply?

Answer

In my opinion, the permissible dimensions are well specified in the manual. These dimensions should therefore be adhered to. In my opinion, only one 3.5 inch drive should be able to be installed with a STRAIGHT POWER 12 750W. I have installed a CORSAIR Shift PSU in my configuration. With this, the cable management goes sideways. With this variant, two 3.5 inch drives can be installed.

Answer

https://www.fractal-design.com/app/uploads/2022/12/North-Manual-V1.2.pdf

Page 27 describes exactly how and how much HDD you can install with which PSU length.

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Question about Fractal North

According to the data sheet, the power supply may be a maximum of 155mm long if you want to use both 3.5 inch HDD slots. However, the Be Quiet power supplies have a length of 160mm, e.g. STRAIGHT POWER 12 750W. How many 3.5 inch HDD slots can be used with a 160mm power supply?