I mean I have a soundcard and it has a volume knob, then windows has volume too, and then whatever application I be using like Youtube or Spotify or VLC has volume knob too, also if I hook up a reciever to a card, it has a volume knob too, so my question is - In this sequence what volume should be left at maximum and what is ok to make lower depending on circumstances?
Again, the thing goes like that - Soundcard-Windows-Application- Reciever (optional).

Put everything else as max volume, and adjust directly from the receiver

So, if I connect headphones to the soundcard then I should put windows on max, spotify on max and adjust just the soundcard volume?

Correct, the device that has direct control over the power output of the speaker/headphone should be the one youre controlling, the rest at max.

Thank you