There’s a bug with the side buttons. After you long press a side button, the next short press won’t do anything. Kind of annoying.
Their “brand-new UI” isn’t much of a change. At least, I haven’t noticed any significant improvements. Toggle buttons are now rectangle, instead of the rounded pill shape, and some icons are different. I think they changed the system font, but I changed it back.
Dark Mode in Neo Reader is an improvement, except that I don’t use that app. Quickly tested it, and it doesn’t seem to invert images, so you won’t see them in dark mode. Systemwide dark mode would have been a significant UI improvement. Hopefully they’ll come up with one some day.
The best improvement I have noticed is the new anti-flicker feature. When using “speed” refresh mode (I think it’s called “balanced” on other devices), the display flickered annoyingly if there was any animation.
This is a Bluetooth issue, not Linux or Deck specific. When microphone is enabled on a headset, Bluetooth will switch to a different audio codec. That codec supports one output channel (microphone) and one input channel, so it will be mono audio. The sound quality is good enough for audio calls but not for anything else. The only thing you can do is to disable the microphone. Or, you can do what people have done for couple decades now: complain at Bluetooth Special Interest Group until they improve the standard.