Same here, I'm on a very legacy v2.2. To enable the iPhone X resolution, you need to add a launch storyboard or specify a launch image with the correct resolution as specified here:
5 Tips & Tricks for Updating Your App for iPhone X
However after doing this, all my sprites appear "smaller" on screen, likely due to the higher resolution and some internal cocos2d scale factor thing, but I'm not sure why exactly this is happening.
If you have any ideas where to look, that would be a huge help! I tried poking around CC_CONTENT_SCALE_FACTOR but I don't really know what I'm looking for.
For example, the ground here takes up the full width on every other iOS device, but not the iPhone X