Figured this out a couple of weeks ago, you can force the engine to cut out by a hard press of the brake when stationary.
Edit.. I think the engine has to be up to temp first as I tried it after first getting in this morning and didn't work.
You’ll see an A with a diagonal line through it on the dash when stop/start is deactivated. Could be due to fluid temps or cabin temperature demand (need engine running for AC compressor). Also gearbox must of course be in D.