I get what you mean just nibble out a bit from between the 2 mounting holes, if that is what you mean, from the above.
Only needs to be 5/10mm at most.
You could prob squeeze in an ssd currently, 2 port sata but usb, 4/5 port sata will all hit the heatsink, unless it has a 5-10mm notch in it.
Still doesn’t fix the extender I purchased that in reality 40pins are not enough conductors for 4x lanes of pcie.
I should be able to fit a 200mm ribbon or maybe even longer and have this thing where ever I chose.
Its also likely the rockpi4 on-board is missing those gnd traces even though likely to be short.