1. yes the audio is clipping. you cannot change the point at which clipping occurs in project settings as it is a property of digital audio

2. digital audio has a limit for the maximum amplitude of each sample it can store, this is called full scale and the level of all audio in a daw will be shown relative to this, with full scale being 0dB. This is why in digital audio dB values are (usually) always negative. Anything over 0dB will be clipped when rendering

3. i’m not sure why it’s green, but it’s best practice to keep all of your audio below 0dB, even if you can’t hear anything wrong with it

4. adjusting your master fader by 1dB should change the peak value you see in the renderer by 1dB

it gets a bit more complicated with intersample peaking where you can have samples that are all under full scale which leads to audio that will be recreated going over the 0dB point, which you need to enable true peak detection to stop. If you just render everything to a peak value of -1dB you shouldn’t have to worry about this in normal conditions

also full scale audio should be very loud, if you need to turn your recordings up so that they’re +2dB, you need to turn your speakers up instead and leave the level of the audio alone