libplacebo new major releases (e.g. going from 6.xxx to 7.xxx) include soname bumps (which should be raised by pkgctl has a warning).
In such cases, you can run sogrep on the built libplacebo package to identify the list of packages to rebuilb against it (e.g. for repo in core extra; do for lib in $(find-libprovides libplacebo-7.349.0-1-x86_64.pkg.tar.zst | sed 's/=.*//g'); do sogrep -r $repo $lib; done; done | sort | uniq).

The list currently consist of:

ffmpeg
jellyfin-ffmpeg
mpv

libplacebo support has been disabled in vlc for the time being (see the related MR), because of incompatibilities with newer libplacebo versions (hence why vlc does not appear in the above list).

Creating ToDos to track those rebuilds (in staging) is encouraged. For instance: https://archlinux.org/todo/libplace-7-rebuild/