Calibrate/profile your monitor, set the RT preview to use the monitor profile, use the default RT Working Profile (ProPhotoRGB) and us the Output Profile as relevant to your output: if it’s for web, use one of the sRGB profiles.
Windows Photo Viewer is colour-managed but Windows Photos isn’t (it doesn’t respect the monitor profile). If you calibrate/profile your monitor, the profiling program should take care of setting the system-wide CM setting for your display. I don’t know about Opera, but I use Firefox and set its colour management policy to respect my monitor profile (type about:config / gfx.color and change the mode to 1 – it will work for everything except video).