Graphics Programmer here.

More likely you would just write data to a buffer (basically an array of whatever element type you want) rather than a render target and then read it back to the cpu. Dx, vulkan, etc. all have APIs to upload / download to / from the GPU quite easily, and CUDA makes it even easier, so a simple compute shader or CUDA kernel that writes to a buffer would make the most sense for general purpose computation like an advent of code problem.

OP is talking about advent of code day 8 part 2 solution. I can’t give you details of the problem (because that’s just to long) but you’re not supposed to brute force the solution because it would take trillions of iterations to get to the right combination.

But the guy in the picture did it anyway.

I forgot to add, you’re in the advent of code community so that alone should be enough context to understand OPs post. The questions the other guy asked are the equivalent of going to a formula 1 community and asking “Who the fuck is Toto Wolff and what does Mercedes have to do with anything?”