With a monopoly, you may very well be making everyone pay for the increased price gouge that comes with monopolies. Not just the customer of that particular product. It depends on the nature of the product.

If it is a component of a more common device or product, basically everyone ends up paying more (HDMI comes to mind). If its an innovation relating to a basic need and gets integrated with the majority of services, basically everyone ends up paying more. If its something that has external implications on the market or wider world that creates inefficiencies, then people functionally make less money because effect people pay more and thus long term this harms spending on a variety of products. If people can’t afford the price gouge and continue using less effective products (assuming they are even available) they likely long term spend more money to make up for the inefficiencies from that.

Monopolies damage things beyond the product that gets monopolized and merely concentrates wealth.

Regardless a subsidy is not the only alternative. That’s still thinking in terms of carrot, and you are forgetting the stick. You can also legislate mandatory R&D in budgets for large corporations based on revenue/profits just as much as you with the punishment of potentially being fined/taxed more.

But outside of that, there is also government contracts. That is, a single payer, (monopsony) generally can get fantastic results out of competing firms. Its largely a major reason why the American Military has historically benefited from such significant technological advancements for nearly a century now.