When will we get an Update that Supports the 8GB of RAM?
Raspberry Pi OS 64-bit is still beta.
The NextcloudPi-Image is based on Raspberry Pi OS (32-bit).
Watch Raspberry Pi Forums (there is a link to the beta-image): Raspberry Pi OS (64 bit) beta test version
Or watch regularly this site until the 64-bit version is released.
Official Raspberry Pi OS Downloads
Do you already have tried the beta and installing NCP via install-script?
curl -sSL https://raw.githubusercontent.com/nextcloud/nextcloudpi/master/install.sh | bash
If this is not working you have to wait or look for an alternative.
When I try to install it on the beta 64-bit version it fails completely.
Do you happen to know how fast the OwnYourBits developers are with such problems? I am certainly not the only one who wants to install nextcloud on the RaspberryPi 4 Model B 8GB RAM.
The developers already investigating some issues. You can also contribute if you want.
Perhaps you can install Raspbian and then Apache2, MariaDB and normal Nextcloud and not NextcloudPi.