Just like other classic consoles on the market that have been hacked, they eventually get Retroarch ported to it. Retroarch is amazing all in one emulator set up that is on multiple systems and it was just a matter of time when Retroarch was going to be ported to the PlayStation Classic.
With the help of CompCom, & ModMyClassic they have released a new PlayStation Boot Menu + RetroArch build as an early Christmas gift. Right now this is only a pre-release/beta with 91 different cores in it, so you might see a few bugs but for the most part, the major stuff works it just needs some fine polishing for those little hiccups. Boot Menu + RetroArch Instructions:
1. Download and install BleemSync (https://github.com/pathartl/BleemSync/releases) following all the instructions including formatting the USB drive as FAT32 or EXT4 and changing the label of the drive to SONY (This won’t be the case soon as it will be built into BleemSync!)
2. Extract the contents of the Boot Menu archive to the root of your USB flash drive overwriting any existing files.
3. Plug USB drive into PlayStation Classic and boot like normal.
4. Using the PlayStation Classic controller highlight the option you wish to launch and press X
Note: “You must restart the system to swap between RetroArch and BleemSync. You must exit RetroArch using the Quit option in the menu (The power button on the console is disabled when running in RetroArch mode).”
Download: PSC Boot Menu + RetroArch Christmas Beta
Download: PSC RetroArch Cores
If you experience any problems with the new Boot Menu + RetroArch you can notify them in their PlayStation Classic support channel in discord here and remember any feedback will help on making improvements/fixes for the official release.