r9000 Dura Ace inner chainring vs r7000 105

As for the inner chainring, is there any difference besides price, weight and style between a DA inner chainring and its 105 counterpart? Are they otherwise compatible, functionally the same and roughly as durable?

There are tremendous durability differences between different chainrings. Quality rings have every single tooth machined from 7075T6 or 7075T651 aluminum. Cheaper rings can use a weaker aluminum alloy or a more crude process for forming the teeth.

Shimano apparently doesn't tell what aluminum is used in their rings, but I don't believe the rings cheaper than Dura-Ace (or XTR) would use 7075T6 or 7075T651.

One way to estimate the material is cost of the ring. If the little ring (34-39T) costs less than 20 euros plus taxes, or the big ring (50-53T) costs less than 30 euros plus taxes, it is highly likely the rings are not machined 7075T6 or 7075T651. Of course there are manufacturers that sell junk at high prices, so this is not a fully reliable method.

I'm usually a big fan of Shimano components, but for chainrings I'd stick with a manufacturer that clearly says "7075T6" or "7075T651". I have at least observed the cheaper Shimano chainrings to wear away in no time.

A 50-53 tooth big ring made out of machined 7075T6 or 7075T651 could last as much as 100 000 km or more if you rotate it often to even out the wear and change the chain religiously. A big ring made of cheaper aluminum could be too worn in 10 000 km.

Here is a list of some chainrings known to be made of good or bad material: https://www.bikeforums.net/bicycle-mechanics/755771-6061-aluminum-not-like-7075-aluminum-theyre-not-even-almost-similar-2-print.html