This is still happening in Xcode 12.2 Beta 1 which was just released. Super frustrating. It seems to only affect building for the simulator though.

This seems to be affecting the App Store version only. I had the GM (209) installed from before, and the documentation viewer works fine there. It also seems to be fine in the recently released Xcode 12.2 Beta 1.

It looks like this is finally fixed in Xcode 12.2 beta 2 (12B5025f). It's not mentioned in the release notes, but I was just able to build for the simulator with no errors.

Thanks for the suggestion Media Engineer. Reported via Feedback Assistant: FB8914573. @pilosof - thanks for sending this workaround. I will give that a shot.

@aldukeman - My bug report to Apple has changed status to "Potential fix identified for future OS update". Hopefully we'll see a fix in the next iOS version.