I designed a little 3d-printed case for the Hifiberry DAC+ ADC Pro with a Raspberry Pi 4. Should also fit the non-pro version. Easy to print and assembles with just the nylon spacers and screws that came with the hifiberry. Should provide a basic level of airflow, and I think it looks ok. Designed in OpenSCAD, so changing the holes to fit other hifiberries should be really simple.
Files at https://www.thingiverse.com/thing:4753525
Also an easy to open version with a hinge is available at thingiverse. Might be useful in case you need to switch jumpers often.