Beware! Christos committed 9b26d309123abf0e90651298b131783ba7d9b945 on main branch of #FreeBSD #ports tree to ignore FreeBSD15 on audio/virtual_oss port and posted heads-up.
https://cgit.freebsd.org/ports/commit/?id=9b26d309123abf0e90651298b131783ba7d9b945

https://lists.freebsd.org/archives/freebsd-stable/2025-September/003305.html

And correlated virtual_oss codes are NOT YET MFC'ed into stable/15.
https://lists.freebsd.org/archives/freebsd-stable/2025-September/003306.html

Christos states he would MFC in 1 or 2 days,
https://lists.freebsd.org/archives/freebsd-stable/2025-September/003307.html

but it means if you upgrade ports including and after the above-mentioned commit on stable/15 including any of ALPHA snapshots before the MFCs are done, you'll lose virtual_oss functionalities.

So hold upgrades of ports/pkgs or `pkg lock audio/virtual_oss` would be wanted in the meantime.