He means idea in the broader sense of nonphysical concept. For example, the patent for a drug is not private property in the same way that a plot of land is. One is a physical entity which can only be owned/utilised by one person or group at a time, and another has no physical properties and can be utilised by literally every single person alive had they the inclination.

Patents/IP/etc only have 'scarcity' because the government agrees to grant a monopoly to a person or corporation. It doesn't have any basis in natural law.

Just because it's not physically present doesn't mean it's not real. Patent represents compensation for time spent researching and developing it.

Without it, you would resort to greater degrees of secrecy.

Sure, it's real, but it is not affected by scarcity. Monopolies are never a good idea, they suit oligarchs at the expense of mankind.

First-movers already have an advantage in the market, this seems to be a natural incentive for R&D. And then also consider that many innovators and inventors do what they do for reasons outside of gaining monetary compensation.

Any consequences of greater secrecy would be largely overshadowed by the advantage of having an actually competitive market in film, tech, healthcare, and etc. Imagine if any manufacturer could produce insulin, or if any film student could shoot their own Star Wars movie.

I'm on a few dumb software patents and they always start with "a server configured to..." given how close software patents are to ideas.

This is the party line, but it just isn't true. Patents are obtained & enforced on ideas all the time, especially in software. PMC is enforcing a patent on the idea of DRM, on the idea of error-correction in streaming video. They never implemented either (beyond a prototype which may or may not have had these features, and never sold).