I was trying to build this version of ffmpeg, and it appears that if the vulkan use-flag is set, it does not try to pull in the vulkan-headers before building the package. I manually installed dev-util/vulkan-headers-1.3.216 and it compiled just fine, otherwise it will complain about not being able to find vulkan during the config checks.
Steps to Reproduce:
1. under the plasma / systemd profile, with vulkan use flag set
2. attempt to install ffmpeg
3. it will complain it cannot find vulkan during the build
4. install vulkan-headers
5. ffmpeg, with vulkan useflag builds just fine.
Request ebuild review.