Hi. As a title said, current Editor.CreateDefaultInspector() overrides entire Inspector UI so if you want to add simple additional button to inspector, you should create all of default insepctor element yourself or using legacy IMGUI container ( New with UIElements in 2019 - How to draw default inspector ).
I thnk UIElements version of default inspector element makes many developers be happy.
A really nice utility would be to be able to have a call that would spit out the uxml (and possibly uss) that would define the default editor.
Often you want a custom editor to be 95% like the default one, but with some changes here and there. If you could automatically generate the default uxml so we could copy that and edit it, that’d be great.
We’d of course have to manually update it once the target script changes, but that’s fine - the alternative is to write the entire editor from scratch, in which case that’d still be the case.
Alternatively, once you switch default editors to be uxml-based, we could generate the root visual element, and then target the things we want to edit with UQuery. That would require the elements to have some identifier we could use to hook into.