First thing: Make sure SketchUp was installed correctly. Quit SketchUp now, find the downloaded installer and right click on it. Select Run as administrator and then choose the Repair option when it is presented.
What is the scale setting in Windows?
A repair or reinstall may just fix things, but if not, try editing this file with a plain text editor (Notepad ought to work):
%LocalAppData%\SketchUp\SketchUp 2019\SketchUp\PrivatePreferences.json
One of the sections in there defines the Materials tray dimensions, and it looks like your one is cut off. Here is how the values are in my file:
(edit: Dan suggested a way to make the code look better, but you’re only meant to be using my text as a guide, don’t copy and paste this into your file):
"Workspace\Trays\Dialogs\Materials": {
"BottomHeight": 314,
"height": 646,
"Splitter": false,
"TopHeight": 478
},