avrdude: ser_open(): can't open device "\\.\COM3": The system cannot find the fi

Hi,
i started using Arduino Uno , installed the Arduino IDE and i can’t upload to Arduino anything.
in the compiler i see the following problem:
avrdude: ser_open(): can’t open device “\.\COM3”: The system cannot find the file specified.
In addition, the PORT button is grayed out

i tried to uninstall and install again and nothing happened
any suggestion how to solve it?

Thanks

What does device manager say when you connect the Arduino? Any yellow triangles?

Is this an original or a clone? For the latter, you might need to install the correct driver.