Most consumer mobo's I see support this even if the setup isn't on the QVL. If a DDR5 motherboard support 4 sticks at all you can probably run 192gb on it so long as you update the BIOS firmware. The problem is running at rated speeds.

AMD tends to be worse than Intel, and I hear people having to run anywhere between DDR5-3200 to DDR5-5200. You are better off running two sticks, because even with 2 sticks you really can't run larger models with acceptable performance anyways, much less with 4.

There is competition to apple on the low end (dual channel fast DDR5) and on the high end (8+ channel like Xeon/Epyc/AmpereOne). In the middle, Apple is sort of crushing because if you run a true 4 channel system you're going to get poor performance if you load up a 192gb model, and if you compare pricing to 96gb/128gb apple systems, there's not all that much of a cost advantage and you have to make a lot of sacrifices to get there. The truth is that Apple really doesn't have all that much competition right now and won't for the foreseeable future.