Other than that, a lot of self-published authors start by uploading their works onto the Kindle (Unlimited) platform, and then marketing via personal blogs, twitter, reddit, etc. These authors can often draw small but devoted audiences – enough to make a reasonable career out of it. Admittedly this is, as you said, an Amazon thing, rather than an independent innovation, but it still works for many.
RavensDagger, One of the authors that I follow, posted an infographic of their 2020 work & earnings: https://i.redd.it/0cur92r6ll861.jpg
No actual earnings numbers, but Pirateaba is probably the highest paid person on the platform with north of 4k patrons at various tiers, although they recently switched to publishing on their own website only rather than using RR.
I'm not super familiar with the space, but I think this is what WattPad seeks to achieve. I know there have been at least a few stories on there that struck it big via Netflix deals.