It switched the code away from remapping keyboard keys to "XF86Audio*", to expecting players to contact the D-Bus daemon and ask to be forwarded key events.
|Multimedia keys circa 2003|
In 2013, we added support for controlling media players using MPRIS, as another interface. Fast-forward to 2021, and MPRIS support is ubiquitous, whether in free software, proprietary applications or even browsers. So we'll be parting with the "org.gnome.SettingsDaemon.MediaKeys" D-Bus API. If your application still wants to work with older versions of GNOME, it is recommended to at least quiet the MediaKeys API's unavailability.
|Multimedia keys in 2021|
TL;DR: Remove code that relies on gnome-settings-daemon's MediaKeys API, make sure to add MPRIS support to your app.