hmm. the usb port on the HH5 is only a usb2.
Have you tried just running with a standard install? The space is tight but sufficient to run OpenWRT and AGH. Its upgrades that use the space and can be mitigated by upgrading manually. OpenWrt AdGuard Home 101 ( DNSMASQ ) - #11 by mercygroundabyss
How did you setup AGH once it was installed?
Otherwise i'd suggest removing the /opt/AdGuardHome/ folder totally and reinstalling from scratch in case something went wrong during install.