mainboards are tied to cpus since they provide the socket for the cpu.
furthermore mainboards are tied to a cpu manufacturer since an AMD cpu is built differently from an Intel cpu, the mainboard "talks" differently to them.
on top of that RAM generation is tied to the CPU you're using, since the controller for the RAM is part of the CPU these days.
your i7-2600 CPU doesn't support DDR4 RAM. there's no way to make these parts to play together
you can't buy a new mainboard for your i7-2600 and then a few months down the line replace your i7-2600 with an AMD cpu. or a new i7-9700 for that matter
if you buy a new mainboard it only works with a supported CPU. So if for example you were to buy a MSI B450 Tomahawk Max today, you'd need DDR4 RAM and an AMD Ryzen CPU for it to work.
if your current mainboard broke and you need a replacement, but you can't afford to swap CPU and RAM as well right now, you'd need to find a mainboard that supports your i7-2600.
CPU + mainboard + RAM kinda form a team that can only be replaced together when you're upgrading after several years unfortunately