Someone on the Lutris forums actually posted a workaround!
posted by thulium
You can workaround this issue by removing C:\Program Files (x86)\Battle.net\Battle.net.11537
Make sure you have a folder Battle.net.11378 in there, if you have that, you can run the launcher again!
I’m fairly certain it will work given you have any other battle net version in there. I had Battle.net.11512 and it worked just fine. In any case, you can always just rename the troublesome folder instead of fully removing it if you’re worried it may not work.
A supposed solution to fix this entire problem was found on the lutris forums to fix the problem without messing with the folder and without bypassing the launcher. If someone could test and report back that would be great. (I’m still reinstalling.)
You need to add the following two libraries to your wine configuration: api-ms-win-crt-private-l1-1-0 and ucrtbase.
How-to: Right-click the game and select “Wine configuration” then go to the Libraries tab and add the libraries from the drop-down.
I had this issue all the time in 2016 when trying to load the Blizzard Launcher. If I got it fixed then, maybe I would have bought a subscription earlier. This is one of the reasons why I would prefer a native Linux client.
This worked beautifully for me. I play on Ubuntu, and have just been bypassing the Bnet Launcher for the last month, as it hasn’t been working. Today there was an update though, and nothing worked. Using this I am now updating and about to head back into the game. Thank you!