You don’t need to connect the app every time. Simply having Carbyte plugged in disables AFM/DFM and Auto Start/Stop. The apps are there for when you want extra functionality, like checking diagnostic trouble codes.
Johnv76 is correct, Carbyte doesn’t void your warranty. In fact, it doesn’t make any permanent changes to your truck. Once unplugged there’s no trace that you were disabling anything.
Carbyte uses a different algorithm. Once it disables DFM, it will keep it fully disabled for the remainder of the ride, even when coasting or coming to a stop.
However, on the refreshed GM models like your 2023 6.2 AT4X, you need to travel at 40+ mph for at least a couple of seconds before Carbyte can disable DFM. Once you reach that speed, DFM will be fully disabled until you switch your engine off. If you never reach 40mph, the DFM will still be able to kick in.