The Alder Lake 12600K is definitely the way to go. A motherboard that supports DDR5 RAM is heavily preferable, but only if you can find DDR5 RAM to buy (DDR4 RAM won't work in those slots). And even then it might not be cost effective at this point. You could also opt to get a DDR4 board for Alder Lake if you don't want to buy new RAM. If you bought your RAM recently, if it's like 3600+, then you won't lose much of anything in games, right now, as benchmarks showed, but you would gimp your ability to upgrade the RAM down the road (but most don't seem to do that).
If you don't want to spend $300 on a CPU the i5-11400 is the way to go. I'd get the Z590 Gigabyte Aorus Elite AX with that since it's just $170 right now. That's a steal right now.
https://pcpartpicker.com/product/YJ...x-atx-lga1200-motherboard-z590-aorus-elite-ax