This might (stress might) be a work around if you have not already deleted your Battle.net prefix and game files while using Lutris as the launcher.
Rename or delete the Battle.net folder in your prefix ProgramData folder.
Change the Game Options → Arguments in Lutris and add
The D3 option is if you don’t have Diablo3 installed, or Pro if you don’t have Overwatch or SC2 or WTCG or Hero - basically any code for a game you DON"T have installed. I have found the default Lutris-7.2 runner to work best with this. Save the configuration and launch battle.net.
After logging in, locate your game, first go to settings → Downloads and Scan for Games then Locate. Once you have located your game, change the Game Updates to Never automatically apply updates then press Done.
All going well, your game is now available and if it was already updated, you should have the play button available. To confirm that this works, shut down the launcher back to Lutris and relaunch it. I have used both D3 and Pro options - the launcher will complain a minute or 2 about the Update agent being asleep before taking you to the game home page which you don’t have installed (this seems to be key, when I used WoW with World of Warcraft install, it did not work). Select your game from the games page and if the Blizzard gods favour you, you will be greeted with your game page, Play button active and the update happening and doing nothing in the background until we can work out what dependency is actually missing for the 8009 Agent.exe. For me, World of Warcraft now launches just fine. Interested if this works for anyone else…