5.6.2 I can't open existing projects

My system is Debian 11. I installed 5.6.2 direct from the kdevelop site

My problem is when I go to open an existing project on my system - say 
project file name xxx.kde4 - the directory listing has all files grayed 
out and I can't open the project file.

If I use the file system browser and right click on the project .kde4 
file it opens in kdevelop but nothing is loaded and it reverts to some 
other project (some older projects seem 'lodged' in kdevelop and I can 
do things with them, but nothing to most of my project files)

What steps do I take to get my version of kdevelop to work with my 
existing projects?

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Jeremy