Viewport Diagnostics Overlay - BCON UI Proposal

Inverted Normals - Identical to the Face Orientation overlay, but from a theme level, just disable the blue coloring. This is preferred by users (and some tutorials even suggest it) because then you can leave it on while you work instead of the blue color obscuring things.

That one has just been tackled! It will be in 4.4 projects.blender.org/blender/blender/pulls/130618

I agree with all other points too, and the add-on is a great prototype, but I think they should be implemented natively for performance as they seem like expensive operations. Similar to how the old "Auto Smooth" feature used to be disabled by default (even though people asked for it to be on) because of how expensive it is to be recalculating normals all the time as you model.

If not adding these things to existing layouts, then making a new one specifically for troubleshooting would be great. This would actually be my preference if I'm honest.

Idea is great, but please, make sure different colors will be used to each one : )

Custom colors to different objects would be nice to.

Something like: RED 255 to the higher poly count model. RED 200 to the second higher poly count model and so on.

In some specific works, a way to "ignore" a mesh would be great, since in some scenarios something considered "heavy" by the code it's necessary.

Another suggestion, is also trigger this idea during all the working modes.

While in OBJECT, show the objects itself. While in EDIT show things like N-GONS or triangles, or vertices that it's attached with more than 5 other vertices. While in SCULPT, show the density difference between geometry, if a human head have a higher poly count (dynatopo for example), this faces will be RED (or something like) and another parts with less polygons can be yellow, orange or a lighter color, something similar to what users have in weight paint, to make it more easy to understand.

And the same to GEO NODES, painting in RED the most demand part of the process.

There should also be an option to select these faces/vertices in order to easily isolate them. This could work for object mode too. For example, in a big scene if you want to just select objects with duplicate vertices or strange normals you can do so. Then isolate the problem objects to fix them more easily.

Could even add an auto fix button where it merges vertices and recalculates normals.

Similar to most of Andrew's suggestions - I often find myself struggling when there are duplicate objects directly on top of one another. It is easy to have duplicates and not realize. Any kind of button that would check for duplicate positioned/rotated items would be great.

Also within the Object State filters in the outliner if we could get one for that filters for the render on/off toggle, that would be amazing.

I don't quite understand On the account of inverted nomals Why don't the Blender command just darken the normalizes on the reverse side? Is it really that hard to implement???