In Wavelab there is plug in simply called gain.
This a simple slider that makes the whole mix louder.
Is this also in Cubase 10.5 ? I can’t find it anywhere.
I’d like something in the output slider to make the whole mix louder.

HI, You can use Pre gain which is part of EQ for each channel- I mean that section with phase shift, LP and HP filter has also pre gain control. Its possible that You have to activate visibility of this section somewhere in channel settings. I hope it helps - more info would be in manual.

Read the Plugin PDF manual. All plugins that are included in your version are listed there, with description of their parameters…