These are the packages that would be merged, in order:

Calculating dependencies... done!
[ebuild     U  ] sys-fs/zfs-2.1.8:0/4::core-kit [2.1.7-r2:0/4::core-kit] USE="nls pam python rootfs split-usr -custom-cflags -debug (-kernel-builtin) -libressl -minimal -static-libs -test-suite" PYTHON_TARGETS="python3_7 -python3_10 -python3_8 -python3_9" 0 KiB

Total: 1 package (1 upgrade), Size of downloads: 0 KiB

Would you like to merge these packages? [Yes/No] 

>>> Verifying ebuild manifests

>>> Emerging (1 of 1) sys-fs/zfs-2.1.8::core-kit
 * zfs-2.1.8.tar.gz BLAKE2B SHA512 size ;-) ...                          [ ok ]
>>> Unpacking source...
>>> Unpacking zfs-2.1.8.tar.gz to /var/tmp/portage/sys-fs/zfs-2.1.8/work
>>> Source unpacked in /var/tmp/portage/sys-fs/zfs-2.1.8/work
>>> Preparing source in /var/tmp/portage/sys-fs/zfs-2.1.8/work/zfs-2.1.8 ...
 * Applying zfs-LegacyVersion-ax_python_dev.patch ...
patching file config/ax_python_devel.m4
Hunk #1 FAILED at 97.
Hunk #2 FAILED at 122.
Hunk #3 FAILED at 131.
Hunk #4 succeeded at 212 (offset -1 lines).
Hunk #5 succeeded at 235 (offset -1 lines).
Hunk #6 succeeded at 244 (offset -1 lines).
Hunk #7 succeeded at 264 (offset -1 lines).
Hunk #8 succeeded at 288 (offset -1 lines).
Hunk #9 succeeded at 300 (offset -1 lines).
Hunk #10 succeeded at 312 (offset -1 lines).
3 out of 10 hunks FAILED -- saving rejects to file config/ax_python_deve [ !! ]j
 * ERROR: sys-fs/zfs-2.1.8::core-kit failed (prepare phase):
 *   patch -p1  failed with /var/tmp/portage/sys-fs/zfs-2.1.8/files/zfs-LegacyVersion-ax_python_dev.patch