Can't see material windows

[DaveR]

See this thread.

Texture import/edit hanging SketchUp

Probably no need to uninstall. You might try going to User/App Data/Local/SketchUp/SketchUp 2019/SketchUp and editing the file called PrivatePreferences.json. Can you see ModalEditMaterialDlg? The User/Appdata directory is normally hidden so you need to make it visible. Just searching for it in the Windows Explorer panel under your username should make it show.