Hopefully it’s not complaining about firmware because that would mean your switch is talking to Ninty. If it is, the latest FW is 14.1.2. I heard you can update your CFW by downloading the firmware from that Darth Sternie Firmware site. Then you can use daybreak.nro (comes with Atmosphere, your CFW, by default.)
if you’re not blocking Ninty using exosphere and dns:mitm, here’s how to set them up:
More than likely you are seeing a game update though. You can continue to ignore it and start game anyway or download the update from your favorite jolly rancher and update it to make the warning go away.