What a great question! I am in the process of figuring this one for myself.
I work full time as a seasoned IT professional and been doing that close to 40 years now. I am one of the lucky ones that really loves his job. Great colleagues, ongoing forever changing challenges, lots of learning to do, loving it.
Till a few years ago I would have called myself a 100% amateur/hobbyist dabbling with synthesizers and relevant technologies. About 4 years ago, the composing Muze hit me full force head on and now I cannot stop writing music, even if I wanted to

. I have a few EPs myself online on practically all the different streaming, download platforms. I have made an EP in collaborating with Gernot (also a member of this forum) and one with my partner Evelien (she sings Lisa Gerrard style/ I play the synths). I am working with a friend producer, who is finalizing the mixes and end mastering to publish an LP (about 12 tracks) towards the end of this year, beginning 2020.
So far on the distribution rights (through Feyir) we made about 3 Euros over the last 3 years. Enough to justify a Prophet X purchase (joking). I pay wherever feasible, who helps me mixing and mastering for publication.
But of course this is only possible because I earn a living and have been doing that for a long time.
I am in the process of actively researching and working out the possible ways in which money can be made composing, publishing, selling music. Perhaps if I succeed I can continue doing this when I retire and augment my (non-existent) pension.
For me the big advantage of going this way is that I can totally explore my own creative path. I have no need to care about what other people think about the music I write and publish, it doesn't matter. I do see this creative development as a kind of prerequisite getting into the business of sound design and composing on demand and/or on specification (like film scoring or writing music for dentists, whatever).
I have found out one thing. Like with most other industries it is very important to make contacts and get to know the right people. This is something I still need to work out in the music / entertainment industry. It is not "what you know" but "who you know". Obviously you need to make a good impression when you do meet the right people. Always good to have a "portfolio" ready on Soundcloud, Spotify, iTunes etc.