Actually you CAN emulate the PS2 on the Pi 4, but the speed is abysmal and the legwork required is insane. The tl;dr version of the story is you need to install Windows 10 using Windows on Raspberry and run PCSX2. SOME games run at playable speeds, but not many. Disgaea 1 and 2, Kingdom Hearts 1 and 2, Final Fantasy 10, and Final Fantasy 12 are playable. There are likely more, but those are the ones I've tested.
Please do not post a support request without first reading and following the advice in https://retropie.org.uk/forum/topic/3/read-this-first