OK, it is the package dracut-pcr-signature and mktemp was added in the commit Various small improvements · aplanas/dracut-pcr-signature@719dad9 · GitHub
So to fix it - manually unlock and mount root (either in dracut emergency shell or booting live image), chroot into it following the usual procedure, disable dracut module
echo 'omit_dracutmodules+=" pcr-signature "' > /etc/dracut.conf.d/disable-pcr-signature.conf
and recreate initrd
dracut -f --regenerate-all
And open bug report on https://bugzilla.opensuse.org/
P.S. you can also include mktemp insead, see man dracut.conf, look for install_items.