There has been an uptick of interest in the NRF52840-CKAA-R RF SoC.
Now we have the NRF52840-QIAA-R in our system, but the ‘CKAA-R’ suffix is not one we carry, it could be special ordered. The main difference is going to be the package type and size

QI = aQFN 7 x 7 package with 73 pins at a 0.5mm pitch
CK = WLCSP 3.544 x 3.607 package with 93 pins at a 0.35mm pitch

AA = is the memory callout, 1024kB of flash and 256kB of RAM
R= Packaging, 13" tape and reel.

So as you can see it will not be a great replacement option. This is just one of those cases where this part is kind of on its own as we have no other options that can match the package size.