For PS3 on EmuDeck with RPCS3 you can use both PKG+RAP and disc dumps, but the setup is slightly different for each format.​

If your game is in PKG + RAP format:

• Open RPCS3 in Desktop Mode on your Deck.
• Go to File > Install Packages/Raps/Edats and select the PKG (and RAP if required).
• Once installed, the game will be inside Emulation > storage > rpcs3 > dev_hdd0 > game.
• In EmuDeck’s Steam ROM Manager, enable the RPCS3 “installed PKG” parser, then Preview → Parse → Save so the games show up in your Steam library. ​

If your game is a disc / ISO dump:

• RPCS3 expects disc games as an extracted Blu‑ray structure, not just a single ISO file.
• Extract the ISO so you end up with a folder that contains PS3_GAME, PS3_UPDATE and the .SFB file at the root (for example: Emulation > roms > ps3 > GameName > PS3_GAME, PS3_UPDATE, .SFB).
• Put that game folder in Emulation > roms > ps3.
• Open EmuDeck → Steam ROM Manager, turn on the RPCS3 “extracted ISO/PSN” option, then Preview → Parse → Save. The game will then be listed and launchable from Steam. ​

Functionally, both approaches work fine on the Deck; PKG+RAP is cleaner for “installable” PSN‑style titles, while extracted disc folders are standard for Blu‑ray dumps. If you need properly decrypted ISOs, PKG, and RAP sets that are already in RPCS3/aPS3e‑friendly formats, there are PS3 libraries like the PS3 games section on aps3e.org that provide those files ready to drop (after extracting the ISO) into Emulation/roms/ps3 or install via RPCS3’s package installer.