All of these are supplied in the standard environment as part of the
SDK now, so there’s no closure difference at build or runtime and
no reason to turn them off.

Upstream is pretty good about using availability checks, and there
are runtime‐checked features for macOS 10.13, 11, and 12 that
are only available if we build with a modern SDK. This impacts,
e.g. hardware‐accelerated video decoding in mpv.

FFmpeg should still continue to build and run on all our supported
macOS releases, with runtime functionality being no worse than before
on older versions.