These numbers are complete guesses. Take this is a grain of salt.

I don't have direct experience here, but from what I've seen from colleagues, a successful hyper casual mobile game at a sufficient level of polish to succeed is multiple years work from 2 developers, and requires a marketing budget (and prior experience of mobile monetisation strategy). You could put out 5 quick casual games just as research / training, not a profitable business model.

Mobile seems very hit or miss. Success is probably over US$10K/month in revenue, or otherwise under US$100 total revenue. One or the other - no in between ?

Steam is not indie friendly these days without a marketing budget. Their algorithms changed last year to amplify games that were already selling, rather than trying to help users discover un-advertised indie games. Again, this makes it very hit or miss. A successful underdog might get $100k on launch and then $1k per month.

The safer bet would be to take a demo of your game to someone else with capital, and get them to pay for you to port it to Sony, Xbox, Nintendo, iOS, etc and pay for marketing, in exchange for most of the profits. They take on the risk and you get paid up-front to do the work... You also get a bigger chance of a successful launch by selling on multiple stores with a single marketing spend.