New Battle.net update Version 14542 breaks Linux compatibility with Wine/Proton via Lutris or Steam and will only display a gray screen.
Workaround is to delete the update folder Battle.2.net.14542
under $wine_root$/drive_c/Program Files (x86)/Battle.net/
and then start the client again.
Update workaround: Set WINE_SIMULATE_WRITECOPY=1 environment variable in Lutris
Thinking about it we may actually have less breakage now as Blizzard has started selling Diablo 4 on Steam provided they implement it well. Does that version come with battle.net launcher as mandatory or is that requirement foregone beside account linking?