Cubase on M1 max to Apples Studio monitor troubles

Cubase 12 audio on my M1 Max usually routed into Genelec 1032 monitors, but today I bought the new 27" Apple studio display from their Regent st store as they actually had one in stock !
Get home and without the Genelecs I figure plug in the Apple monitor via Thunderbolt cable and I can check the new screens sound quality. All audio plays fine, including project audio from Reason.

Now the trouble - pulled up ‘studio setup’ in Cubase, selected ‘built in audio’ and changed it to ‘Studio display speakers’ … nothing. Whilst the project was running I reset to ‘Built in audio’ and got sound again from the M1.

So what am I doing folks ? could it be the thunder bolt cable is not compatible with Steinberg app’s. What has me is that it work perfectly with Reason.

(nothing to do with this thread, but ReCycle is working perfectly on the M1Max ! How can that be ?)

Thanks in anticipation of the answers.