That update was most likely the 10.7 ArcGIS Coordinate Systems Data update. It's fairly large as far as updates go, 985 MB. I'm not aware of any patches or other updates out for 2.3 yet.
That being said, this update shouldn't cause an otherwise perfectly functioning ArcGIS Pro client to gridlock. It doesn't take up that much space in the install directory.
You might take a look at Task Manager when you open existing projects and see what's there. Do the performance issues not occur when using new projects after the update?
OK, thanks for letting us know. Would you be able to log a case with Technical Support on this (888-377-4575)? If this is related to a 2.3 problem, we need a record of it through a support case. They can troubleshoot the issue and, either fix it if this is specific to your install, or log a bug if this is specific to a general 2.3 issue.
Were you able to get your prior projects working at reasonable speeds? I am experiencing a noticeable slowdown on all of my existing projects and creating new ones is not ideal. (Although since we cannot lock multiple layouts my projects were all bloating anyway but I don't want multiple bloated projects).
It just took a project over 3 minutes to open with two simple layouts open.