How to quickly check if peaceful mode enable/disable

You cannot check if it was enabled or not. However, what you can do is enable/disable it with the console.

Go to options and look at the keybinding to open the lua console. You can find the binding in the game tab.

Once you open the console, type the following command

/c game.player.surface.peaceful_mode=BOOL

Replace BOOL with TRUE if you want to enable it or FALSE if you want to disable it.

You can have a look at all the other commands here.

Keep in mind that using console commands will disable achievements.

You can use the following console command to check whether or not peaceful mode is enabled:

/c game.player.print(game.player.surface.peaceful_mode);

Keep in mind that using console commands will disable achievements, but you can save your game, run the command, and reload your game afterwards to avoid achievements from being disabled.