These are the packages that would be merged, in order:

Calculating dependencies ... done!
Dependency resolution took 1.57 s (backtrack: 0/20).

[ebuild     U  ] dev-util/spirv-headers-1.4.357.0::gentoo [1.4.341.0::gentoo] 559 KiB
[ebuild  N     ] dev-util/vulkan-headers-1.4.357.0::gentoo  USE="-test" 3298 KiB
[ebuild     U  ] dev-util/spirv-tools-1.4.357.0::gentoo [1.4.341.0::gentoo] USE="-test" 3436 KiB
[ebuild  N     ] dev-util/vulkan-utility-libraries-1.4.357.0::gentoo  USE="-test" 1311 KiB
[ebuild  N     ] dev-util/glslang-1.4.357.0:0/16.4::gentoo  4310 KiB
[ebuild  N     ] media-libs/vulkan-layers-1.4.357.0::gentoo  USE="X -test -wayland" 8180 KiB

Total: 6 packages (2 upgrades, 4 new), Size of downloads: 21092 KiB