No, RetroPie cannot be installed on the SteamDeck, it's not using a compatible Linux distro.

If you have a SteamDeck you may want to take a look at EmuDeck for something similar to RetroPie.

@muldjord

I understand that i can load it along side it. But it would be nice to have inside of steamos and just click on it from the library. It seems that RetroArch is jumping on it. That's why I asked, but they seem to be doing it from the windows point of view. like i said it would be nice to have it support in steam not a side load. that's all.