@Tibsz
Hi,
Typically, when the video mode is set to Auto, the camera switches between Day and Night modes automatically based on ambient light conditions. If a Tapo C420 does not switch to Day mode automatically, it may be that the camera is in a dark environment, even during the daytime.
If the camera is in a well-lit area during the day but won't switch to Day mode automatically, please select Day mode on the camera's live view page. Is the camera's IR LED turned off? Does the camera display a colorful page? Please send us a screenshot of the live view page for checking.
You can try to reboot the camera (remove the battery and reinsert it) and see if it switches the video mode automatically.
Best Regards