The latest version of the RPi OS which was issued on 8th November has seriously broken Pi Presents. As an amateur developer I get no notice of these changes.
Fortunately the previous version of the OS, based on Debian Buster, is available and should be used for Pi Presents Beep and Gapless. It appears Buster will receive security updates and bug fixes for a few years. The OS is available here:
https://downloads.raspberrypi.org/raspios_armhf/images/raspios_armhf-2021-05-28/
For the technicaly minded Bullseye has removed mmal/omx and video players that rely on it – omxplayer and the VLC facilities I use to embed videos. It has also replaced FKMS with KMS which alters control of the displays.
Pi Presents 
FYI: I had a similar issue, i.e. OMX dependency, with pi video looper and current version of bullseye. I took a risk with rpi-update. Afterward, it compiled fine and works.
All your work on this is much appreciated. I used this to make a vintage radio play at an exhibition in Derby.
Have you contacted the RaspebrryPi org on this matter? Perhaps an update may be on the way. I say this because I much prefer to use the latest OS releases,
i wonder when the 64 Bit OS version will arrive??
Pi Towers has been contacted and I am waiting for details of the changed interfaces to VLC. It will probably take a few weeks to upgrade PP to Bullseye. The blog post was mainly to warn people not to use/upgrade to Bullseye and to tell them where Buster an be found.