Intellectual property is shorthand description for a very particular type of exclusive right. Compile enough exclusive rights and you might have a big competitive advantage that nobody else can overcome in a particular market.

But not every exclusive right is actually intellectual property. Sometimes it's just normal property, like owning a particular building that is really good for filming particular scenes in. Or owning a particular unique car that you can rent out to those who want to use it. Or it might not be property at all, like the simple right to truthfully declare that a particular movie was directed by Christopher Nolan.

IMAX's competitive moat includes intellectual property (its trademarked name, presumably a bunch of patents in its equipment), but also includes a bunch of physical things: a production line and supply chain for a very specific format of physical film, physical equipment like cameras and projectors and editing hardware/tools, etc. And some of it includes other intangible rights or legal powers (contracts, rental agreements, financial arrangements that make it hard for others to compete).

So both of you are right that IMAX keeps its competition at bay through both intellectual property and other property rights, and other financial and legal powers and relationships (like, I'm sure they work closely with these A list directors). All it it blends together into a dominant position in their niche space. Most movies just choose not to use film at all, and even a bunch of other film formats are still in use. But IMAX still stands out for their specific format.

gatekeeping for elite film makers instead of being an open standard for artists and auteurs

But I don't think imax are producing the cameras they just own most of them. That's how it is with the projectors anyway. It is an IP problem if imax is stopping others from making their own cameras in that format but I think it's just the monumental cost of spinning up production lines for niche goods that is preventing that. So market forces sure, and likely imax is rent seeking but 70 mm format cameras are not their intellectual property.