Calculating dependencies... done!
[ebuild  N     ] app-eselect/eselect-opencl-1.1.0-r4
[ebuild     U  ] x11-drivers/nvidia-drivers-440.82 [440.59]
[blocks B      ] app-eselect/eselect-opencl ("app-eselect/eselect-opencl" is blocking dev-util/opencl-headers-2020.03.13-r1, dev-libs/ocl-icd-2.2.12-r3)

 * Error: The above package list contains packages which cannot be
 * installed at the same time on the same system.

  (app-eselect/eselect-opencl-1.1.0-r4:0/0::gentoo, ebuild scheduled for merge) pulled in by
    app-eselect/eselect-opencl required by (x11-drivers/nvidia-drivers-440.82:0/440::gentoo, ebuild scheduled for merge) USE="X acpi driver kms libglvnd multilib static-libs tools -compat -gtk3 -uvm -wayland" ABI_X86="32 (64) (-x32)"

  (dev-libs/ocl-icd-2.2.12-r3:0/0::gentoo, installed) pulled in by
    dev-libs/ocl-icd[khronos-headers,abi_x86_32(-)?,abi_x86_64(-)?,abi_x86_x32(-)?,abi_mips_n32(-)?,abi_mips_n64(-)?,abi_mips_o32(-)?,abi_riscv_lp64d(-)?,abi_riscv_lp64(-)?,abi_s390_32(-)?,abi_s390_64(-)?] (dev-libs/ocl-icd[khronos-headers,abi_x86_64(-)]) required by (virtual/opencl-3-r1:0/0::gentoo, installed) USE="" ABI_X86="(64) -32 (-x32)"


For more information about Blocked Packages, please refer to the following
section of the Gentoo Linux x86 Handbook (architecture is irrelevant):

https://wiki.gentoo.org/wiki/Handbook:X86/Working/Portage#Blocked_packages