... is it possible to activate/deactivate debugging for specified virtual hosts (for example phpmyadmin phppgadmin host)?

Are you using localhost or another domain name to access all of your sites, or different domain names for each site?

Some people use the same domain name, most commonly localhost, to do local development. That will share the debug cookie and can cause a variety of problems.

Also ensure that Tools > Run & Debug > Settings > Break on start is unticked. I always have it unticked, then I use F9 to start debug sessions for just the sites that I do really want to debug.

Tools > Run & Debug > Settings > Break on start is unticked.

As all projects are running on a dedicated developement server "localhost" would not be an option. All projects have a different domain using a special local TLD.

Any ideas?

What debugger settings are you using in php.ini?

If you access a virtual host without PhpED running, do you get a message in the browser about not being able to debug or does the site run normally without debugging?

Does debugging start on the very first PHP statement (Break on start) or does it start on a statement that may be causing an error (Break on errors) or exception (Break on exceptions) ?

debugger.enabled can be set via phpvalue in httpd.conf

An what about cli Scripts? Is it possible to disable debugger for a certain script?

what scripts are "cli"?
php itself does not support any per-file or per directory settings.