Isn't it dangerous to boil carbonated water in a kettle?
Whenever I boil water in my kettle, I close its lid. Does this close lid constitute 'under pressure' (and so danger) emboldened beneath?
No danger! If you are worried about flames, carbon dioxide is not flammable. If you are worried about explosions, gas is not released so fast to cause an explosion.
For comparison, you can free much more energy per time by overheating plain water.
So nope, no danger, even if you place a lid on it (assuming that the lid is free to bump and release CO2/aqueous vapor, but even if it wasn't I doubt that it would be much more dangerous than doing the same with plain water).