[pimterry]

There are absolutely Ruby jobs out there that will pay your bills, and it's absolutely a successful ecosystem with which you can build effective modern products.

That said, in 2020 if you're picking a language, I don't think it has the most jobs available (probably JS), or the best paid jobs available (something ML, maybe Python), or the most interesting jobs available (up to you). For similar reasons, I'm not sure it's the best language to pick for a new product - it doesn't have the largest community or most momentum nowadays, it's neither the forefront of powerful tech nor the backbone of rock-solid boring tech.

If you already know Ruby, or you just want to learn it anyway, it's definitely not a bad choice. If you're choosing afresh though with no specific reason to pick Ruby, it's probably not the right choice.