Hello,
Thanks for the answer.
I think I found your issue. It’s probably linked to the fact that you have 2 duplicate entry in your /etc/hosts file with this content:
::1 localhost
The issue is that, slapd try to resolve localhost from the host file and this return theses entries: 127.0.0.1, ::1, ::1. And so slapd don’t detect the duplicate and try 2 time to bind on ::1. The first time this will work but the second time this will fail with the error Address already in use.
So, what I suggest you is to remove one of your entry in your host file which map ::1 with localhost. Than you can restore the change that you did in /etc/default/slapd. And try systemctl restart slapd than systemctl status slapd and this should work.