Capitalism does not reward those whose labor makes a greater impact, it rewards those who own Capital

It does reward those who make a greater impact. Entrepreneurs don't get rich if their use of capital doesn't have a far reaching impact.

Look at Elon Musk, he was able to use his capital to build compelling EVs and rockets, such that both became very popular products with far-reaching impact. Yes, he himself didn't build the EVs or the rockets, but his capital was necessary to fund development of those products. If he didn't invest in those products, we likely wouldn't have had such growth in those markets because he essentially created the demand for those products.

There are a ton of success stories that could be labeled "good" or "bad," but at the end of the day, they all have far-reaching impact through some mixture of capital and work that wouldn't have happened without both.

The problem with capitalism isn't capital itself, but how it's accumulated. My argument is that capital accumulated from entrepreneurship using capital generated by the individual is the system working at intended, and capital accumulated across generations is a corruption of that system. In other words, individual ownership is desired, inherited ownership is not.

why would anyone accept that unless there was threat of violence?.

Consensus is the alternative to centralized threat of force. Various anarchist constructions have ideas on how that could work.

I personally reject all anarchist constructions as fanciful, but there are extant systems that demonstrate that (e.g. cryptocurrencies).

FOSS is a rejection of ownership and profit, simple as.

No, FOSS is a rejection of restrictions.

Richard Stallman didn't create GNU and the GPL to "socialize the means of production," he did it because he was annoyed at not being able to modify software that you bought. He didn't particularly care who owned the software, only that he could modify it for his own personal use and share those modifications with others. He didn't want to own the original code, only his changes to that code to the extent that he could share his changes. In essence, he believed producers shouldn't be able to restrict their users through licenses, and this was largely a new thing under the Copyright Act of 1976 (i.e. "fair use" as a concept).

The whole intent was to preserve hacker culture, and is very similar to the Right to Repair movement for physical goods. Like the GPL, Right to Repair doesn't seek to change ownership rights to the product (i.e. you don't get a patent grant), it merely seeks to enable users to make modifications and repairs on their own without needing to go through the original vendor/manufacturer.

That said, FOSS attracts people from all over the political spectrum. Socialists like it because it looks like shared ownership (even though it's not), libertarians like it because it empowers the individual, capitalists like it because it's a way to share the cost of maintaining a common system (i.e. forcing competitors to share fixes), etc. But at the end of the day, it's not an economic system, it's not even a change in ownership, it's merely a license to share code. Don't make it more than it is.