If you regularly update your Kali machine and use Openvas you could run into this error: the default postgresql version is not 13 required by libgvmd
It’s because there are two versions of postgresql running at the same time. Since postgresql is using a TCP port it cannot be the same port for both versions. Openvas is expecting version 13 running on TCP port 5432. When you get the error possibly version 12 is using this port. So the fix is to change the ports by editing the following files:
sudo nano /etc/postgresql/13/main/postgresql.conf and change the port to 5432.
sudo nano /etc/postgresql/12/main/postgresql.conf and change the port to 5433 (or any other port which is free).
sudo systemctl restart postgresql
Then start the Openvas service and hopefully it will run without any errors.