I'm also having trouble replicating the appearance of the UIToolbar
on colored backgrounds as it was shown in the WWDC presentation.
It is true that it automatically gets the glass look in iOS 26. This requires no special code; just add a UIToolbar to your view. But it looks decidedly different than in Apple's video. Here's what I get:

I tried to adjust the colors using backgroundColor
and barTintColor
on the UIToolbar. But they have no apparent effect in iOS 26 (unlike in iOS 18).
It's possible that this is just a bug in Beta 1, and I'll file a bug report. But if anyone has been able to achieve the liquid glass effects in UIKit as shown at the top, please share.