No idea where you got the timeline. A former Blizzard employee who worked on it stated that development for D3 started in 2001, back at Blizzard North. Development started with Windows and Mac versions in mind and it went through several iterations before it was first shown to the public in 2008.
Since D4 was announced back in 2019, you can bet they've been working on this behind closed doors for years. And if they had a Mac version on mind, this would already work on the Mac right now. This is very common in the game industry, work begins long before a game is first announced to the pubic. And not just the game industry, it's everywhere. Apple had a Intel version of macOS years before they announced the switch from PPC to Intel and the same can be said for the current transition.
If D4 doesn't work for macOS right now, then there's no way it will happen in 2023. Add another 5 years to that, if you're lucky. I don't say it will happen 5 years later, this is all based on how long software development in the gaming industry usually takes and that's also the best case when there's money to be made (on top of development costs).