Level reduction outside of Cubase 11 Pro

Recently, for no apparent reason, my Audio-Mixdown (wav 24 bit) files and all other sound medias, are quieter. But, when I play them and turn on/open Cubase, they play back at the same levels as my original Cubase track mixes.
Only seemed to happen when I upgraded to (Mac Mini Intel) OS Mojave. Now using Ventura - same problem.
e.g. If I play music on my Mac only, it’s quieter. When I just open up Cubase, (separately but simultaneously) the music (YouTube etc and my own Audio wav and MP3s) increase in Volume to the level it should, and used to be.
I believe all my sounds should be using my A/D UR44 and I’ve checked my Mac sound settings and can find no solution.
Any help/advice would be appreciated very much.