I just built a laptop and I always choose Mint. I used the XFCE spin and it failed me. Everything worked well except the second monitor screen. I just could not get it to display proper 1080p. I tried forums and changed a bunch of configurations.
I ended up getting Fedora on it and it worked out of the box. Oh well. Fedora it is then.
In my country we mostly use WhatsApp and it has a specific option in the menus that says 'in chat notification sound' which does exactly what you are looking for.
What I would suggest is try another messaging app that is more feature rich such as textra. I bet they do a better job at handling notifications than the default app.