Let's start by checking to see if any error reports were written on your machine as *.dmp files. These can typically be found at: C:\Users\<User Name>\AppData\Local\ESRI\ErrorReports. If there are any crash reports here, feel free to attach them, as we may be able to extract some information from them.
Also, can you just verify that your machine meets the minimum requirements with the Can You Run It? tool for ArcGIS Pro2.3.
Leo, are you on a desktop or laptop?
Can you check your graphics card driver and update if possible?
Are your Display settings set to DirectX or OpenGL? If DirectX (which is the default) what happens if you switch to OpenGL?
Leo and Deena:
Did these crashes occur for aprxs that were created in a previous version of Pro? Were the aprxs originally created by importing mxd files into the aprx?
Did these crashes occur for new aprxs that were never opened in any other version than 2.3?