Tons of opportunity out there, but success is as much about social media as it is about the music. In many ways, it's just like selling books. Beyond a decent product, you have to engage with your audience/fans.
The simple analysis is that there are tons of amazing musicians out there, like an unbelievable number - it's crazy. But playing isn't the same as writing memorable songs. Turns out, it's kind of hard to do. So, yes, the market is super-saturated, but not nearly as much as it might appear.
The important bit is that the music business is changing. It's no longer album based. It's all about the single. Sure, down the road you package them just like a box set for additional revenue, but it's the singles that keep you relevant - and TikTok length hooks are even better.
It's just like writing. If he wants to do it - then he needs to just jump in and start uploading and sharing. But the most important part of social media engagement is that you have to be consistent. Don't start until you have the time for regular posts, like as close to daily as possible. Instagram is a great way for musicians to interact with fans and network with other musicians by posting little song snippets and general music stuff. YouTube is another great platform. But you have to have the songs available before you can market them. And make them available everywhere.
Distrokid is a good start. It's like D2D for music.
I'd recommend
Adam Ivy and
Damian Keyes over on YouTube for music industry marketing advice. Go by the more recent videos, though. The Indie scene has changed so fast that some of the older advice is no longer relevant.
Oh, and just like anything these days...Branding and Messaging are everything.