Can't double click on desktop icons

I’m using dietpi on my Raspberry Pi since version v6.7 and everything worked fine. The last days i dared to update dietpi, it’s now v.6.25.3. Now i’m not able to start programs with the shortcut on the desktop (MATE). I have to rightclick the icon and “open”, but a doubleclick is useless - nothing happens.
That happen with all my desktop shortcuts, except if i create a new folder on desktop. Double clicking on a new created folder offers me to rename the folder.

Whats wrong now? Did somethin happen with the MIME type list? I’m not really an expert in using linux, but maybe somebody can help me fixing this problem.