Is the Hajj obligation waived for someone who intended to perform Hajj and went for it, even if he believes he made mistakes in the rituals or committed sins he is unaware of? And is he required to perform Hajj again?

Sins do not invalidate Hajj. The perpetrator must repent and desist from them. To review what is required in the rituals, one can refer to concise books on Hajj rituals or fatwas related to Hajj on the website. It is best for the questioner to specify what Hajj actions they omitted or what prohibitions they committed, so that they can be informed of what is incumbent upon them.