OP, …”I gave it some thought and started wondering what defines "new music" in the context of this conversation?”.
For me, music I never heard before. I started in the 60’s and 70’s with rock… then discovered Jazz, (stopped listening to rock) the jazz fusion, the classical, then world, world fusion… I’m sure a few more. About 20 years ago I added rock back in to the mix occationally.
Now I listen to new albums as they are released on Qobuz in most genera. I skip hip hop and rap. So, my horizons are ever increasing. If I find an album I like I will work backwards in their history if the have one… and try “similar” bands. I probably listen to 70 % music I never heard of two years ago. Some from the 1950’s most from the last decade or two.