Well, it's nice to have a new friend, in the xkcd-2881 sense. :) My app is also ObjC (as you can tell from the fact that it dates from 2016!) I doubt that has any effect on how the app icon is treated, anyhow. tvOS 17.3 release notes (https://feedbackassistant.apple.com/news/7213) make no mention of this. I guess I will file a bug report, I mean a Feedback, and then submit the app as is.

It passed this morning. (Also, I checked the behavior after installing 17.3 on the device. No change.)

For what it's worth, the problem went away on a tvOS update, without me doing anything further about it. I believe it looked correct on 18.0, and still looks correct on 26.