Yocto provides mounting points for two 60 mm fans under the GPU. Depending on the radiator size of your GPU, you can attach fans up to 25 mm thick to these points.
The sum of the fan thickness and the radiator height, starting from the PCB, can be no more than 48 mm. As a reference, I've made a table below with all the radiator dimensions of most of the popular low profile GPU's.
Advised fans
There aren't many quality 60 mm fans, but we're lucky that Noctua, one of the best fan manufacturers, has a great one. The NF-A6x25 PWM is probably the best fan you can get when deshrouding your GPU.
Controlling fan speed
GPU's tend to use different fan headers than regular case fans use. To control the fan speed based on the GPU temperature, you can buy an adapter. However, many cards define a high minimum fan speed on their header, so it is much easier and advised to use a fan header on your motherboard. You can then control the speed very precisely using software like Fan Control. You can find an in-depth guide to controlling fans based on GPU temperature with Fan Control here.
Note on the RTX A2000
The RTX A2000 is the strongest and most recent low profile GPU and a popular choice for the Yocto. But the blower style cooler makes it unsuitable for deshrouding. While it is a pretty quiet card, its minimum fan RPM can be annoying, so I came up with a custom heatsink solution that enables you to deshroud this card!
