> For my taste, this standard macOS 26 Liquid Glass treatment muddies the boundary between UI and content way too much

Exactly this. Apple's marketing of Liquid Glass was about separating navigation from content so that content is more prominent, but in practice it's the exact opposite: animation, flashes, shadows, saturation. The navigation draws so much more attention than the content, especially so in macOS with that floating sidebar thing.

The Notes app, the Music app, and more. Why is the sidebar drawing so much attention? The increased roundness and padding also actively REDUCES the amount of content that is visible. People have compared iOS 26 with whatever iOS version was on the iPhone 5, and despite the iPhone 5 screen being only 4 inches (60% of the size of a regular iPhone today), it shows MORE content than today's iPhone with Liquid Glass.

It really feels like Apple has lost its head. How do people test this, compare this, and say "this is good, this improves the user experience"?

I've been a Bike user for a couple years, and I assume the sidebar and calendar are new additions for Bike 2.0? I've never seen them, and I couldn't find them mentioned on the website, so I believe that's the case. In my opinion, the fact that it's hard to design this well should be an indicator that these features shouldn't be added! I already have a ton of general purpose notes/calendar apps (currently on Obsidian), I don't need another. Bike should stick to its focus: Being really, really good at outlining.

I'm not a user of that Bike but "Here’s what Apple’s Notes looks like on macOS 26" that looks fine.

I don't see a reason to go full transparency, no surprise that if you ask an AI to do a thing in a style it goes over the top with that style.