horde I think the largest single source of issues is users who figure it's ok to skip some part of the process, especially if it's a technical detail.
For example, the instructions say not to use a browser installed via Snap or Flatpak. But clearly some users don't know how their browser was installed, so it's easy to skip past that part, and then it won't work. Or the ever-popular "favorite USB cable" syndrome: hey, it works for pulling photos from my old phone, and the original Pixel cable is down in the basement, so.... If that kind of thing is solvable by UI changes, great!
In theory there could be more situational handholding... if no compatible USB device shows up, and the browser is running on Windows, it could specifically suggest installing Google's Windows fastboot driver.
A couple times people have reported that they didn't realize that the buttons on the page are buttons that should be pressed in sequence (I guess they don't look like native app buttons?). But I think skipping parts of the instructions is probably the big source of trouble.