@Kamen Sotirov ,@Thierry RAZAFINDRAKOTO Thanks for your patience on this.
Upon investigations,there were changes made at the power automation end. when any user with no license related to Power BI/Power Apps/Power Automate try to edit the custom connector then the error message is observed. To check the license you can navigate to\ AAD --> Users --> License. Power automation team is still working on the issue and for now you can leverage the workaround editing the custom connector using the ARM template.
Deploy a Logic Apps Custom Connector Using ARM Template.pdf
I have attached the instructions shared as .pdf in my comments you can refer to them.