If I’m away for a few hours the output settings (Built-in Line Output) will select my monitor’s speakers which is connected via DisplayPort. If I’m away for more than a few hours (overnight) the settings will switch to Built-in Speakers from my preferred External Speakers.
Thank you for your report. This is a system limitation with MacOS. When your Mac sleeps, it drops the connection to the DisplayPort, this in turn causes DPS to default back to built-in audio.
I will pass this along to my engineering team to check if there is a way we can somehow “remember” when DisplayPort is the desired output device and have that selection persist after MacOS drops the displayport connection.