what does it need to make the RTX 4090 compatible with tools like VanitySearch, BitCrack, etc... ? Is this something we can fix ourselves by just adding a particular ccap file into the sources of the program so it can compile? Or does it need something on CUDA side? Any clues ?
It's the compiler that doesn't support the 8.9 compute capability, not the program. Just upgrade CUDA toolkit to version 11.8 or newer.