Every time I want to open a file or start an application, the previous action is executed.
As I am not able to describe the problem properly, I want to give an example:

• I double click on a file "mypdf.pdf" -> nothing happens
• I double click on a file "myvideo.mp4" -> "mypdf.pdf" opens
• I double click on video again -> the video opens

Same with the start of applications (e.g. with KRunner):

• I type Dolphin in KRunner -> nothing happens
• I type Settings in KRunner -> Dolphin opens up
• ...

This weird behavior started after I updated many packages yesterday.
Restarting does not help.
I currently use KDE neon 5.22 with the 5.4.0-74 Kernel.

I am pretty unsure, where I could even start to track this bug down.
If you have any ideas, which logs/settings/configs could be relevant, I would be happy to share them!