@leocg
Thanks for the link.
I didn't list all the actions I performed, I followed also the suggestions in the link in advance https://support-vpn-pro.opera.com/hc/en-us/articles/4829369755793-I-m-unable-to-connect-to-Opera-VPN-Pro-servers-What-can-I-do-
no success :¬(

On other devices (Windows 11 laptop, Android smartphone) the vpn service works very well.

The main problem is: I'm not able to (re-)install the client.
It is possible that the reason lies in the Windows updates; my machine has the latest fixes installed.

The service of VPN Pro seems to be broken

An installation is suggested in the VPN menu bar

The install process run 'very fast' . . to fast. So the error was not corrected by the installation.

Checking the Windows event log:
Messages

• Product: VPNPro -- Installation failed.

• Das Produkt wurde durch Windows Installer installiert. Produktname: VPNPro. Produktversion: 2.0.17.0. Produktsprache: 1033. Hersteller: Opera Norway AS. Erfolg- bzw. Fehlerstatus der Installation: 1603.

Repeated installation attempts

• by turning off ANTIVIRUS
• by truning off FIREWALL
  -> no success

Repeated installation after . .
Clearing network caches by

• netsh int ip reset
• netsh int ipv6 reset
• netsh winsock reset

Remove all network adapters in device manager

• Uninstall WAN Miniport drivers (IKEv2, IP, IPv6, and so on . . )

Up to this point nothing helped

Question
How can I remove all the installation information of VPN Pro ?

• registry ?
• program directories ? (there are no entries in app installation of system control)
• user space
• more . . ?