In recently install OMV8 on a Pi5 with Trixie. I followed the documentation step by step and accessing it from my Win11, iPad and iPhone worked from the first second.
You already got the correct links to the official documentation for your setup. What I always do before doing anything, entering commands in the SSH client (in my case Windows Powershell) etc., I read the docs completely(!!!) from the first to the last character and make sure that I understood everything. In case I dont understand something or not being sure, I ask questions here in this excellent forum with a lot of nice people.
And no, I'm not a IT/Linux/OMV-Pro, I started with the Pi5 2 month ago and have meanwhile successfully setup 2 Pis, one with Nextcloud and the other with OMV. So dont give up!