When I open Captivate 2019 the update missing font box opens but does not display anything and I can't close it so I'm stuck and can't do anything. This happens when I open exercise files, real files, or a blank projects. I'm on Windows 11 and Captivate 2019 v11.8
From the screenshot it looks like you are using another theme than the default Captivate theme in a non-responsive project.
Did you change the default theme?
If you updated from a previous version like 11.5, can you please try to clean the Preferences? Find the subfolder 'utils' under the installation folder. Close Captivate and run CleanPreferencesWin.bat. Restart Captivate and see if you still have the same issues.
I've moved this from the Using the Community forum (which is the forum for issues using the forums) to the Captivate forum so that proper help can be offered.