Comment 5 for bug 2058179

Anybody who wants fix right now can do
git clone -b linux_6.8_compat_splice_copy_file_range_fallback https://git.launchpad.net/~antst/ubuntu/+source/zfs-linux
cd zfs-linux
dpkg-buildpackage -rfakeroot --no-sign -b

it will build all related packages, then install locally built zfs-dkms package as
apt install ./zfs-dkms_2.2.2-0ubuntu8_all.deb