I use a Fritz!Box with a OVM5 on a Raspberry Pi 4 with 8GB RAM.
Now I realized, that this is not neccessary and 4GB RAM would be enough.
I changed the SD-card to a Raspberry Pi 4 with 4GB RAM and it did not showed up in the Fritz!Box list of connected devices.
I attached a monitor to the Raspberry Pi and see, that OVM started, I see the same eth0 IP-address as I expected but I was not able to login via admin and password.
[ OK ] Started Hostname Service
[ *** ] A start job is running for Wait for Network to be Configures
...
[FAILED] Failed to start Wait for Network to be Configured
...
openmediavault 5.6.2-1 ....
...
MEDIA login: _ (cursor blinks)
^ this is what I see on the screen
But with admin and the correct password I do get the message
No directory, loggin in with HOME=/
This account is currently not available
It asks for login+password again. I cannot reach a command line for whatever check of the network / dhcp / hostname problem that occured by changing the hardware (= changed LAN-Adapter/MAC address).
I tested the SD card with its OVM5 installation on the 8GB Raspberry Pi 4 again, eveything works fine. I can see it in the Fritz!Box and can connect via https://Hostname or IP-address
Back to the Raspberry Pi 4 4GB: If I do not login with admin but with a normal username, I can start omv-firstaid and network-reparation (first entry), but do not seem to have the rights for special setups.