If I remember correctly, OMV takes the whole drive for the OS as well.
I switched to Proxmox a couple months ago from OMV and am glad I did. I love the ability to really experiment with pretty much anything without impacting the services already running. I’ve been tinkering with Home Assistant, got Blue Iris on a Windows VM after Frigate wouldn’t seem to play nice for me, and have added a few other services I didn’t even know existed when using OMV. Scheduled backups are very nice as well.
It’s pretty straightforward to set up and there are lots of tutorials and documentation if you get stuck somewhere. I’d recommend it, coming from a pretty basic user with limited experience outside of Windows.