You have to remove ntp and then try again to install omv with the script.
ntp wasn't installed (anymore), for whatever reason. Re-installation via script hasn't fixed the issue.
However, in the end I was able to fix it. I used sudo apt purge lvm2 to fix my "broken" apt, which also removed all openmediavault packages.
Then I installed OMV again via
wget -O - https://github.com/OpenMediaVault-Plugin-Developers/installScript/raw/master/install | sudo bash
and I'm now able to login again. My configuration is also still there, thanks guys