Until some days before ClassicShell functioned very well on my PC with Windows 10 Pro x64, but more recently I get the message 'This app was blocked because of security reasons', see attached picture (german)

! The message says 'An administrator has blocked the execution of this app' and the so called editor is 'Not trustworthy'!
My username has all rights of an administrator and is the onlyone administrator besides the main administrator.
I have de/reinstalled ClassicShell but there is no change, ClassicShell is blocked. But why? Is there a problem with the certificate? How can I repair ist?
Can anyone help, please?