I tried reinstalling OMV on a Raspberry 4 several times today. I always have the problem that the web GUI is not accessible (Google Chrome error message: "ERR_CONNECTION_REFUSED").
I have always used the latest "Raspberry Pi OS Lite" (Release 4 March 2021) and the installation script for OMV.
In my last try I really did everything exactly step by step as described in the instructions "Adden-B-Installing_OMV5_on_an R-PI.pdf" (incl. SHA check, H2testw, ...).
The "sudo service nginx status" via SSH/Putty looks OK at first glance "Active: active (running)".
The /var/log/nginx error logs are empty.
The /var/log/openmediafault folder is also empty (is this OK?).