Hi
Eelco •,
Welcome to Microsoft Q&A forum and thanks for using Azure Services.
As I understand, you want to connect with pgAdmin to Azure Database for PostgreSQL Flexible Server.
Since the server is in a virtual network, you can only connect to the server from other Azure services in the same virtual network as the server. To connect and manage the server, let's create a Linux virtual machine. The virtual machine must be created in the same region and same subscription. The Linux virtual machine can be used as an SSH tunnel to manage your database server.
Refer the documentation here for complete details: Create an Azure Linux Virtual Machine.
Hope this helps. Let us know if you have a different ask.
Thanks