HyperPixel 4 - Speaker icon disapears

With a fresh install of Trixie there is a speaker icon on the menu bar to adjust the volume.
I then add the line “dtoverlay=vc4-kms-dpi-hyperpixel4” to the end of /boot/firmware/config.txt

When I reboot the speaker icon is no longer there.

How can I get it back again?

Thanks

Mick