--- mpv 0.38.0 ---
2.3 - partially revert the changes from API version 1.27, remove libmpv as
the default VO and move it to the bottom of the auto-probing order.
This restores the prior behavior on all platforms other than macOS,
but still auto selects libmpv/cocoa-cb on macOS if it was built with
support for cocoa-cb.
from libmpv API changelog
so we should set libmpv as vo explicitly.