I normally use 350°C or so; it doesn’t matter if the component gets damaged while it’s being plucked out with tweezers. Higher airflow can heat up the part quicker and reduce the time and thus spread of heat, but if not directed properly, you could blow passives off the board. I’d definitely choose hot and quick vs. low and slow, both for soldering and desoldering.
Adding flux (I prefer a gel-type rather than a very thin fluid) and applying gentle movement with tweezers can help, best to slide along the length of the pad rather than prying, as that could detach the pad from the board. Sometimes adding extra solder to the pins/pads can also work.
Even though the LEDs were sealed, if they were bought years ago, they could still absorb water over time through the packaging and release that as steam during soldering. This might have also been a factor when building your MatriX, though humidity warnings typically apply to oven reflow.
