Hi !
Sorry if I explained incorrectly. I'll try to reply to both.
The guide isn't telling you to create a user before installing OMV. We can't write something for everything a user might do before installing OMV. That is why we tell people to install OMV first.
Indeed, but I did not create a user before installing OMV. When flashing raspberry pi OS using the official raspberry pi flashing tool, a user is created by default, with sudo privileges; root doesn't even get a password set up and cannot log in. So, that user is pretty much the only way to use the Pi, and OMV gets installed by that user, using sudo (the instructions correctly reflect this). Therefore there's no extra step taken. In fact, I'm fairly confident that I literally flashed the OS, logged in via SSH, and immediately updated the system with apt, called the preinstall, rebooted, and called the main install.
That single user that is set up by the raspberry flashing process is then automatically visible in the list of users in OMV, without any action required. BUT it's not obvious to new users like me that for this particular user, I'll need to run smbpasswd manually because that's the user through which I followed the instructions.
1. Flash an SD-card with Rasp. PI OS.
(Then)
2. Install users of your choice, configure WiFI, add additional non-OMV packages, etc., etc.
3. Install OMV.
Where #2 is concerned, it is IMPOSSIBLE to to predict or anticipate what users many do, at any point, before, during, or after:
As per above, step 2 for me was basically nothing. I flashed the os, plugged the device in (incl. ethernet cable, so no wifi setup even), logged in via ssh and moved on with step 3.
It's relatively easy to provide samba access to existing Windows users on the LAN.
Fixing the issue was trivial once it was clear what was happening. However I did struggle in understanding it was happening, from the lack of warning in those raspberry-specific instructions, and the lack of particular warnings in the UI about this user being "somewhat different" because not created through the UI, but by the raspberry install + OMV install together.
Hope that clarifies!