Hello lamine50,
Thank you for posting in the Apple Support Communities. I understand you are having problems with the low light photos and videos on your new iPhone 11.
It sounds like you may need to verify your Night mode settings.
“Take low-light photos with Night mode
iPhone 11 and iPhone 11 Pro turn on Night mode automatically when the camera detects low-light situations. The Night mode icon at the top of the display turns yellow when the feature is active.
Depending on how dark the scene is, your iPhone might take a Night mode photo quickly, or it might take several seconds. A number appears next to the Night mode icon to indicate how long the shot will take.
To experiment with longer Night mode photos, tap the Night mode icon. Then use the slider above the shutter button to choose Max, which extends the capture time. When you take the photo, the slider becomes a timer that counts down to the end of the exposure.
For the best results, hold your iPhone steady until the capture completes. You can get even more detail and less noise in very dark scenes, such as night sky photography, by keeping your iPhone completely still. Try placing your iPhone on a solid and secure surface or using a tripod to get the longest possible Night mode exposures.
Night mode is available when you use the 1x camera.”
You’ll find this and other helpful camera features in the resource I’ve linked below.
Have a good one!