Thanks @Fogmeister, we did try that and it didn't work.
We could style the ActionSheet buttons, but not the title.
Thanks @stephencelis, we haven't tried it in Xcode 13 yet. I'm not surprised that it now says that's not supported, given our attempts yesterday.
However, thinking about it: we started down this path because we couldn't implement an action sheet without a title as shown here.
Unfortunately, SwiftUI doesn't seem to support an ActionSheet without a title.
I'm guessing we'll need to drop down into UIKit.