Note that the riscv64 patch is also missing from Focal (20.04), and the package also fails to build there. Upstream included initial support in zfs-2.0.0, so newer Ubuntu releases should have it by default:
$ git describe --contains 4254e407294b211f3399da2ee131b45fe9f4ac80 zfs-2.0.0-rc1~665
Note that the riscv64 patch is also missing from Focal (20.04), and the package also fails to build there. Upstream included initial support in zfs-2.0.0, so newer Ubuntu releases should have it by default:
$ git describe --contains 4254e407294b211 f3399da2ee131b4 5fe9f4ac80
zfs-2.0.0-rc1~665