Corrupted update (15.4.1) software preventing iPhone XR restore

Hello:

Halfway through restore of iPhone XR (MacBook Pro, Catalina), a yellow/white triangle popped up, stated: “The software for the iPhone “iPhone” was corrupted during download. Disconnect and reconnect, then try again. Make sure your network settings are correct and your network connection is active, or try again later.” (BTW, both iPhone and my Mac were up-to-date prior to restore attempt, and I'd backed up iPhone and turned off Find My.)

I followed the instructions: disconnected, reconnected, etc., and on second attempt the same window popped up, again, this time 1/4 way through restore.

So, I went into iPhone settings > General > Storage > Update, found the update and tried to delete it... it won't delete.

Q: How do I delete a corrupted software update on my iPhone XR that won't delete when I press "Delete", so that I may, finally, restore my device to factory?

Your sage advice and wisdom on this issue would be greatly appreciated.

Thank you!