You need to install Steam if you don’t already have it installed, then follow these steps.
Step 1.
Within Steam, add Battle Net as a Non-Steam game, you are choosing the Battle.net.exe executable, not Diablo III.exe (!! very important !!),
Step 2.
You need to update the ‘Target’ shortcut in Steam as follows:
"C:\Program Files (x86)\Battle.net\Battle.net.exe" --exec="launch D3"
Assumes Battle Net is installed in the default folder during installation.
Take note of the --exec="Launch D3" appendage, this instructs Battle.Net to open D3, but it seems I still have to open it manually click Play from the Bnet launcher.
Rename the game to Diablo 3 and change out the icon/background artwork afterwards.
Step 3.
Setup your Controller profile, found in Properties → Controller tab. There are some pre-made settings out there you can import, but you’ll want to spend about 1-2 hours refining your profile to make common tasks less painful, ie. looting and salvaging, opening the map, etc. Try to mimic Diablo 4’s arrangement for continuity.
If you’re going full gamepad mode, I highly recommend setting the Left Joystick behavior to Mouse Region.
The time investment in configuring the controller will make playing the D3 PC version tolerable on a gamepad. I’d probably quit trying if I stuck with one of the publicly available profiles.
Step 4. (Optional)
Other game settings that are unrelated to controller support, but important to discuss:
Integer Scaling: you’ll want to enable it in AMD Software Adrenalin on this title (Diablo III.exe). Set your Windows Desktop to 2560x1600, in Diablo 3 Option set the video mode to Fullscreen Windows (1280x800).
Legion Performance Profile: Cap the framerate at 60fps and set the CPU profile to 10-11W, OS Power Mode is set to Efficiency. On my device, this seems to be a sweet spot for long, uncompromised play sessions.