Here is how to Copy the Steam Deck Save file from the Dragon Age Origins Prefix to the Dragon Age 2 Prefix.

Dragon Age Origins has had 2 releases on Steam, the first Release was the Standard Edition which was removed from sale and replaced with the Ultimate Edition, depending on which version you have in Steam changes the folder you copy your save file/folder from. Below in the File paths I've included both versions corresponding folders. Find out which version you have and follow these steps.

In desktop mode, Open Dolphin File Explorer (Folder Icon on Taskbar). In the File Explorer Window that Opens select the 3 Lines top Right Corner, in the menu that pops up Tick Show Hidden Files.

Still in file explorer, in the left menu select and follow these folder paths, go to

Home - Deck - .local - share - steam - steamapps - compatdata - 47810 (Dragon Age Ultimate Edition) or 17450 (Dragon Age Standard Edition) - pfx - drive_c - users - steamuser - documents - Bioware - Dragon Age (Copy this Dragon Age folder)

Still in file explorer go back to the Compatdata folder. Which is

Home - Deck - .local - share - steam - steamapps - compatdata folder and find the 1238040 Folder, inside the 1238040 folder go to pfx - drive_c - users - steamuser - documents - Bioware Folder and Paste the Dragon Age Folder copied earlier.

You will now have both Dragon Age and Dragon Age 2 Folders inside the Bioware folder.

Run Dragon Age 2 and the game will now detect your Dragon Age Origins Save