I really like the size of the displayed toolbar icons in beta 4 now (set to smallest).
The icon for "Open a workset" is now also more homogeneous.

Yes, they are better, but I don't like it, because these smaller icons are blurry.
Maybe 3 different icon sizes (default, smaller, and smallest) is better,

I agree. I'm using light theme and Beta 4 looks musch better than beta 3.

I only wonder why the top of Objects window is not aligned with the top of SQL window.