Got the answer on another forum:
It is a bit late to do it in .onAppear, appearance should be changed definitely before affected view is created, so do it in init:init() { UITabBar.appearance().barTintColor = UIColor(named: "barBackground")} Worked like a champ!
dmiannay
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I decided to move in another direction with my application. This issue is no longer relevant and can be ignored. Merry Christmas!