Prices of 9700K and 9900K are so inflated, that you'd likely be better off buying a new B650 and 7700X cpu, or an Intel 13700K or KF on a B760 mainboard...
One should not pay exorbitant prices for outdated CPUs solely to utilize an existing mainboard...; selling off the old Z370 mainboard should allow you to buy a decent cooler for your 13700K.
I'd also look hard at AMD's B550/5800X3D combos, more than competent for years to come, IMO...; you can always look at a 14700K for a few extra cores over the 13700K if price is not too much higher...
Good luck whichever way you choose to proceed, of course!