The statement was published through Blizzard’s own blog, and TurboHUD4 was targeted only. TurboHUD4 is one of the additions we have stated above and Blizzard had to make an announcement in order to prohibit the usage of HUD, if players persist with their decision to use the HUD, they will be banned from Blizzard’s online servers. Suddenly, the mods in every caliber have drawn the interest of Blizzard and there might be heavy fines for the ones who use it. These additions do not interfere with gameplay as their only duty is to deliver important information about health, enemies, magic power, and more during combat. There are some very detailed overlay and HUD- heads-up display- mods available on modding websites like ModDB and Nexus. Meanwhile, Diablo IV is rather a grind-y title, some players would like to have excessive information about their playthrough. For the uninitiated, vanilla settings mean the stock settings a player would get with the game, anything added to make gameplay better would be a third-party setting and it's usually endorsed by many developers.

Although there haven’t been any issues regarding the usual gameplay, Blizzard is now warning people to not use any third-party mods that enhance the game more than it should do if you were to play on vanilla settings. These include bug fixes, quality-of-life changes, DLC preparation, etc. After the successful launch of Diablo IV, Blizzard is taking measurements and drawing a route for what is expected for the title.

Blizzard's stance on diablo 2 mods