nik Collection 8 plugin funktioniert nicht

Please describe your issue a little bit more detailed.

Which plugin do you try to open?

Which way you're using to open Nik? Via the Plugin symbols or as a filter?

Try to a complete and clean (by using the Nik Cleaner Tool) reinstallation of the Nik Collection. 

https://support.dxo.com/hc/de/articles/5138248326173-Anleitung-Nik-CleanupTool-nur-Windows

https://support.dxo.com/hc/de/articles/5138943110557-Anleitung-NikCleanupTool-nur-macOS

Just an idea: First try to reset the preferences of Photoshop using the steps described here:

https://helpx.adobe.com/photoshop/using/preferences.html#reset-preferences

It's recommended to backup your settings before resetting the preferences.

See here:  https://helpx.adobe.com/photoshop/using/preferences.html#backup-photoshop-preferences

@anitas42637124 

For help with the Nik plugin, contact DXO for support:

     https://support.dxo.com/hc/en-us/

I've moved your post from Using the Community to the Photoshop forum.

Jane