Some thoughts; just my 2 cents:
a) Making money with video games is damn hard nowadays. I've seen some people on mastodon who dev in full time or near full time and seemingly live in financial dependency of their partners, parents or friends. If I break down the wage per hour, I had a by far better outcome as a street musician (allthough I was lousy) than with our games (slight in the reds if we count in what we paid for steam and the server for our website until now, and that is harmless - I have read about more than a few people who lost some thousand of dollars to the unity or unreal asset store). If you are searching for a niche to make some bucks, nearly everything else will likely work better.
b) I had similar concerns, but believe me: Having your source liberated will help you, not the other way around. For some people being FLOSS is something like a sign of quality, and the FLOSS community is by far more supportive than the general independent games community. Assets are another quarrel for me though: If it is more or less "placeholder" art I don't care, but I don't want to see the game art my partner in crime did for our games used in some non-effort game or be sold in some asset pack.
c) While I agree with Shockstah that quality is important: The average quality of libre/open source games is in fact above average. I play a lot of unknown indie games, and try to find a game per week to write a positive review about. I have a lot less trouble finding one since I started to use the "OpenSource"-Tag at Itch as a base for my searches; while there are still many half-finished or lousy games, the rate of good games tagged with "Open Source" is much better. Many of these have a open source but a unclear license status, though.
d) If you think about making a multiplayer game, you are in for frustration. There are countless multiplayer indie games with empty servers.
e) The problem for independent artists, be it music, movies, games, or whatever is the accelerating consolidation that takes place in the whole culture industry. Only if you play by the rules and go the full way (or have a massive streak of luck and are "discovered" on other ways) you'll have a chance to play in the reach of the big shots here, else you are likely to be ignored. This is system immanent. Deving games, doing movies, creating pictures, making music, and so on outside of this total market orientation and outside of your primary occupation is an act of rebellion in itself. This seldom pays, doesn't matter if you are working closed or FLOSS.
Hope I don't sound to negative. Making games is a great hobby, but its one that you likely do just for fun or not at all.