A very similar question was asked recently How to disable instance and cube source selection in TM1 Widget Cube View
For now there is only the option to disable the entire toolbar in advanced options.
"cubeView":{"toolbarVisible":false}
But we have a ER (which hopefully should be available in the Feb 2024 release) to individually toggle each component in the cube viewer toolbar on or off.
In the meantime the only option is to selectively hide toolbar components is to use custom CSS and I see from your screenshot it looks like you already did this for instance, cube and view dropdowns. So you would just need to do the same for the view definition button.
Or if you use full MDX rather than a cube view then the toolbar and view definition drag & drop zones are all automatically hidden.