Below are parts of my design.
Using KiCad, I have problems using both VCC (5V) and 3.3V power, both from Arduino Mega pins.
If on U6 (flash) I connect 3 and 7 I get a similar error, so I guess I did something wrong regarding the PWR_FLAG settings. I also tried using the VCCQ (it also has a round symbol like VCC), but then I get different errors.
What should I change in my schematics to use both 3.3V and 5V without any ERC errors?