Focus Energy works correctly in the simulator or failure as in the original games? It will increase the chance of critical damage if I use it in the simulator?
Focus Energy is not supposed to work in the simulator, and as far as I know, it doesn't either. You can test it if you want by using Jolteon with Focus Energy. If you fail to crit more than once, it's not working.
PO's RBY OU tier uses Yellow cartridge mechanics, in which Focus Energy is glitched. IIRC Focus Energy works properly if you set your gen to Stadium (in which Focus Energy was not glitched). (Funnily enough, setup sweepers actually slightly benefit from a glitched Focus Energy boost thanks to how crits work in RBY, but most things that learn Focus Energy in RBY are shitty anyway and the couple that aren't - Jolteon and Nidoking - don't have setup moves in the first place.)
Thanks, but unfortunately Focus Energy does not work in the simulator, as well as in RBY cartridges, I think this bug should be fixed, because the real intention of the developers of the games was that Focus Energy really worked.