Hello everyone,
I have tried to install ZFS (apt install zfs-dkms), but this failed, becasue the following link is not there:
#ln -s /usr/src/linux-headers-5.4.0-4parrot1-common/include/linux /lib/modules/5.4.0-4parrot1-amd64/build/include/
After this command the installation was succesful!
Greetings,
Robert