Headphone icons gone

Mixxx 2.3.0-beta was updated Saturday and now I find I cannot listen to the master channels with headphones as there is no option to switch to them. Or at least i cannot find them.

Any suggestions as to where/how please. link to screenshot with no headphone icon

https://imgur.com/EOVrN4Q

in the top row are buttons for the major GUI components, like MIXER, EFFECTS…

Thanks I must have missed clicking Mixer, what a dummy :thinking: