Just 1. The ram. As mentioned, 12thGen is still in early adoption stages, and that includes DDR5. Currently there's no real advantage for gaming, it's pretty much an identical situation as DDR3-2133/2400 was when DDR4-2133/2400 first dropped. The better DDR3 matched heads up to the new DDR4. But eventually that changed and DDR4 now hits speeds of 5000MHz, big difference.
Early adoption puts the 12thGen pricing far cheaper to go with DDR4 boards, the ram is considerably cheaper, easier to get. But in the near future when DDR5 matures, all those 3200-4400MHz DDR4 kits will not be on the same level as the 6k,7k or even upto (purportedly) 10k MHz DDR5.
And Zen4 is supposed to drop later next year, putting an even higher demand on DDR5, which will drive prices up, think scalpers and early adopters sucking up anything like gpus are now.
So you'll spend a good amount of money to be left behind. DDR5 users will be seeing higher fps in general. Only solution to fix fps being purchase a DDR5 board and DDR5 ram, leaving you with a DDR4 board and ram which few will want and there'll be a ton of them on eBay as others try and sell off their junk to recoup losses.
I'd say that's a disadvantage, although it won't become evident until later.