I'm also trying to figure this out. Some thoughts/questions raised: Does it uses ShortcutTileColor values for this colour, or hex codes, or the name of a icon in asset catalog, or something else? Does it require things like systemImageName to be specified for the Shortcut? Which images are used for systemImageName? SF Symbols? The Shortcuts app has its own set of icons. If it's these icons and not SF symbols, is there a list somewhere?

Please file a feedback. Perhaps reference this post and my FB number above.

Are you recreating the AVSpeechSynthesizer again when coming into foreground? I'm now trying something similar to your code above (recreating the synthesizer every X utterances). The only other side effect of this is need to preload the voice again to avoid a delay on the first utterance.

No response at all yet. My feedback still says "Similar Reports: None".