My picture blue screen after snap by flash (iphone x)

Try a forced restart of your iPX:

Press and quickly release the Volume Up button. Press and quickly release the Volume Down button. Then, press and hold the Side button until you see the Apple logo. When it appears, release the Side button, wait for your device to restart, then test it.

If nothing changes, since your iPhone is still on warranty, have it inspected at your most convenient Apple STore or Authorized Service Provider:

Apple - Find Locations - Location Selector

Regards

Giulio