Master Buss is always at 0.
Control Room knob is set to 0 too.
When I put main monitors on Outputs->Stereo they don’t pass throught the Control room. It is still set to 0 but is irrelevant.
Is normal that the volume on Outputs->Stereo is way louder than Outputs->Studio->monitor1?
No.
You do disconnect the controlroom, before you connect the main out, don´t you?
Only if you disconnect the port connections, or turn the controlroom fader down, otherwise the sound still goes through controlroom (and additionally through main out) → therefore the increase in volume.
When done correctly monizoring through main outs annd controil room out gives the same volume level given faders are set at same level.