I can't hear audio in youtube when Cubase is open.

[ShikiSuen]

You can use FlexASIO driver instead:

Sampe Rate Help

Sorry to hear you’re having sound problems, @gregclarkmusic. Of the two settings you have there, I’d suggest choosing the 16-bit 48000Hz option. Once you’ve done that, run Dorico again and go to Edit > Device Setup to make sure that the same sample rate is chosen there; if it shows 48000Hz already selected, try opening the drop-down to select a different rate and then return to the original one after a moment. If you still have no joy, I’ve seen @Ulf recommend people try the alternative FlexASI…