I've seen some other folks express similar thoughts on the Parts Manager and I'd like to expand on some of those concerns.
I think I understand what the intention of the Part Manager is, to make a Single Source of Truth for controlling and configuring everything, but I feel that this comes with a greater harm to usability.
In KSP1, there was a direct connection between what you clicked and what you saw/controlled. Right clicking a tank brought out a connected window so there was no confusion about what was being changed and how it related to the rocket.
The Parts Manager in KSP2, however, creates a visual disconnect. Whether in the VAB or in flight, you click on something and suddenly a window pops up. It may have auto-expanded the section relevant to the part you clicked, but for me it still takes some time to find it and even then, there's only a subset of options available especially if we're talking about something like a fuel tank which might require me to alternately go to the Resource Manager.
Making a disconnect interferes with my enjoyment because I spend less time flying or building the rocket and more time 'dealing with' the interface.
If this is a temporary UI meant to make the game usable during development, it's great for that. If it is intended to be a replacement for the UI style KSP1 had, I feel like it's a step backwards and I hope consideration is given to addressing this.
Ideally, the UI should be working for us, not the other way around.