FEhler PHtotoshop Fehler 21

@Manuela36301435lqw0 try uninstalling Photoshop from the Creative Cloud app, select to keep the preferences and then install it again

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

If this doesn't help pleas give us more and detailed informations about your issue and system.

What you've done or try to do before the error occur?

Please provide a copy of your 'System Info'. This can be get from the Photoshop menu item Help > System Info. There's a copy button in the System Info dialog. Press this button and paste the info into your next forum post.