From what I am reading, the 8700k will be a bit of a bottleneck at 1080p in Warzone 2, but overall should still give you a nice upgrade. Also keep in mind that the PCIe gen 3 on your motherboard will be a slight bottleneck as well for the GPU.
My advice: you could always buy the new GPU now, and try it out. And you can still have it for when you do a full platform upgrade later.
Another option, depending on what board you have, would be to upgrade just the CPU to a 9900k, if you can find one used for a good price. This would give you 2 more cores and the clocks a bit higher as well, without having to swap everything out. Though you may need to do a BIOS update first.
Personally, I would get the card first, and see how it does, should be a good upgrade for COD. You can always look into future upgrades after.