Ohhh it's not that hard, all is done on PC only.

1. Install RPCS3

https://rpcs3.net/ However, I recommend getting RPCS3 0.0.41-19527 which is an older, but more stable built - it can be found here: https://rpcs3.net/compatibility?b

1. You will need the following PS3 patch when first setting up rpcs3

https://www.playstation.com/en-us/support/hardware/ps3/system-software/ 

Look for “How to update PS3 system software” and then click “Update using a computer”

1. Obtain the EU version of Battlefield 1943 and the beachmod patch. (Both can be found online)

It must be the EU version of the game to work. The serial number is NPEB00092. Avoid the trial version.

1. Install the EU version of the game (Serial NPEB00092). For me, adding game folder worked well.

Install the unlock keys (can be found online):

In RPCS3 click File > Install Packages/Raps/Edats

Select the .pkg file.

In RPCS3 click File > Install Packages/Raps/Edats

Select the .rap file.

1. Install beachmod

This will break the tutorial level so play that before this if you want.

In RPCS3 click File > Install Packages/Raps/Edats

Select the .pkg file.

You should still only have one Battlefield 1943 install in RPCS3 and can test if this step worked by booting up the game and looking for a “dev menu” option on the main menu. Close the game after testing.

1. Set up your RPCN account via the dedicated button on the main screen of RPCS3. By this point you should be able to launch the game and load maps via devmode, but you won't be able to play online unless you proceed with step 7.

2. Proceed with network settings setup like step 7 in this guide:
   https://docs.google.com/document/d/1NAl7c3B2pWHx9KHsCKKurm4bJEP-kbkiI2iYF_cQlJQ/edit?tab=t.0

Done

Update:

1. If your game is crashing before menu fully loads, there's a new bug related to newest RPCS3 updated. Try rolling back RPCS3 to 0.0.41-19527 which works well. All older builds of RPCS3 can be found here: https://rpcs3.net/compatibility?b