You install battlenet as a third party app through steam/proton (lots of guides online) then you launch it, install D2, and you are done.
I've finished act 5 on the regular difficulty both in D2 and D2R using this setup. I never tried multiplayer in D2 but i can confirm it works in D2R.
This was on an x86 pc though. I found this post on Reddit that might help:
"There is a locked thread in this sub from about 7 months ago referencing a YouTube video from ETA Prime. The video discusses how to install Diablo 2 on a pi4. I'm posting this because I had some challenges when following the instructions, which I figured out how to work around. Hopefully this will help someone. Here's how I was able to get it to work:
On a Windows PC:
You will need version 1.13c of Diablo 2 (and expansion if desired). I can't tell you how to get that installer. You can't download it from Blizzard because their version comes pre-loaded at a newer version number. Note -- You absolutely must find v1.13c. I tried several other versions without success. There's an installer that I found for 1.13c which doesn't require a CD which is important.
You will also need a product key for the base game (and a product key for the expansion if desired). You can purchase these from Blizzard's website.
Run the installer for the base game. Don't start the game after completion.
Run the installer for the expansion pack. Don't start the game after completion.
Go to the folder where you installed it (e.g., C:\Program Files (x86)\Diablo II)
Copy all files and subfolders to a folder on your pi (e.g., /home/pi/diablo2)
Download the modified MESA package from the site referenced on the screen at 1:16 in ETA Prime's video https://www.youtube.com/watch?v=3PhMCxywP7g
Extract the MESA package and copy the extracted files to your pi in /home/pi/mesa
Download libd2game_sa_arm.exe.so.xz from the site referenced on the screen at 1:16 in the same youtube video from ETA Prime (https://www.youtube.com/watch?v=3PhMCxywP7g)
Extract libd2game_sa_arm.exe.so from the .xz file and copy to the pi's Diablo 2 directory (e.g., /home/pi/diablo2). Google how to do this if you aren't sure. I can't remember the exact syntax. I extracted it using a standard command from the Linux command line but there might be a windows tool to do this too.
Then, on your Pi4:
Boot to the Raspbian GUI
Open the terminal and enter these commands (lines starting with $ are commands to be entered):
$ sudo apt-get update && sudo apt-get upgrade
$ sudo apt install wine
$ winecfg
The configuration tool will open. Set resolution to 800 x 600.
Open terminal and use these commands
$ cd /home/pi/mesa/lib/arm-linux/gnueabihf
This is where I needed to go off-script to get the installation to work. The MESA package libGL.so.1 and libglapi.so.0 files did not work for me; I had to replace them with other versions contained in the MESA package.
$ cp libGL.so.1 libGL.so.1.bk
$ rm libGL.so.1
$ cp libGL.so.1.2.0 libGL.so.1
$ cp libglapi.so.0 libglapi.so.0.bk
$ rm libglapi.so.0
$ cp libglapi.so.0.0.0 libglapi.so.0
Go to the diablo2 directory (e.g., $ cd /home/pi/diablo2)
$ nano script.sh
This will load the nano text editor. Enter the following into the editor (without the bullet number "1.") This script will be used to start the modified libd2game_sa_arm.exe.so executable with Wine using the MESA drivers.
LD_LIBRARY_PATH=/home/pi/mesa/lib/arm-linux-gnueabihf LIBGL_DRIVERS_PATH=/home/pi/mesa/lib/arm-linux-gnueabihf/dri/ GBM_DRIVERS_PATH=/home/pi/mesa/lib setarch linux32 -L wine libd2game_sa_arm.exe.so
CTRL+O to save. CTRL+X to exit the editor.Run the following command to execute the script (note the period! )
$ . script.sh
Diablo 2 should load and run. Works great on my pi4B with 4GB RAM."
Formatting got messed up, sorry