On the Dell G5 SE 15?
Honestly, not sure.
Since the cooling design is not exactly what I would call 'adequate', I don't think drilling holes into the back casing would necessarily improve temperatures because the problem (before the BIOS update) was down to poor power management by DELL and poor cooling assembly implementation (or not taking into account the fact that 7nm has a higher transistor density, which by default will generate higher temperatures).
At any rate, with the BIOS update, the problem has been 'fixed' for the most part so the temperatures are staying in an expected range.
If you were asking in general about drilling holes in the back casing of a laptop... for some laptops, that might work, for others, it could be a double edged sword (because while it may improve overall temperatures on the CPU and GPU, the temperatures on some other components in the laptop [such as the VRM's] could be affected for the worse which could result in problems down the line).
With the bios update, the DELL G5 SE 15 is not a bad machine. A bit slower compared to where it should be if Dell bothered to adapt the cooling to the hw, but otherwise an affordable gaming laptop which can be used for productivity.