Debian: ZFS installation error: Module zfs not found in directory /lib/modules/4.19.0-14-amd64

I installed ZFS on Debian, but can not get it working. --- I try to install zfs this way: 1. I added this to /etc/apt/sources.list :

deb http://deb.debian.org/debian/  buster main contrib non-free
deb http://deb.debian.org/debian  buster-backports main contrib

2. apt update and apt upgrade 3. I installed these packages: buster-backports, zfsutils-linux, zfs-dkms, dpkg-dev, linux-headers-$(uname -r), linux-image-amd64 4. And at this point problems accured. --- I get these error when calling modprobe:

root@server /dev# modprobe zfs
modprobe: FATAL: **Module zfs not found in directory /lib/modules/4.19.0-14-amd64**

` This is in my journalctl:

Feb 19 13:33:46 bytserver systemd: Starting Install ZFS kernel module...
Feb 19 13:33:46 bytserver modprobe: modprobe: FATAL: Module zfs not found in directory /lib/modules/4.19.0-14-amd64
Feb 19 13:33:46 bytserver systemd: zfs-load-module.service: Main process exited, code=exited, status=1/FAILURE
Feb 19 13:33:46 bytserver systemd: zfs-load-module.service: Failed with result 'exit-code'.
Feb 19 13:33:46 bytserver systemd: Failed to start Install ZFS kernel module.
Feb 19 13:33:46 bytserver systemd: Dependency failed for Import ZFS pools by cache file.
Feb 19 13:33:46 bytserver systemd: zfs-import-cache.service: Job zfs-import-cache.service/start failed with result 'dependency'.
Feb 19 13:33:46 bytserver systemd: Reached target ZFS pool import target.
Feb 19 13:33:46 bytserver systemd: Condition check resulted in Mount ZFS filesystems being skipped.
Feb 19 13:33:46 bytserver systemd: Starting Wait for ZFS Volume (zvol) links in /dev...
Feb 19 13:33:46 bytserver zvol_wait: The ZFS modules are not loaded.
Feb 19 13:33:46 bytserver zvol_wait: Try running '/sbin/modprobe zfs' as root to load them.
Feb 19 13:33:46 bytserver systemd: Started Wait for ZFS Volume (zvol) links in /dev.
Feb 19 13:33:46 bytserver systemd: Reached target ZFS volumes are ready.
Feb 19 13:33:46 bytserver systemd: Starting ZFS file system shares...
Feb 19 13:33:46 bytserver zfs: The ZFS modules are not loaded.
Feb 19 13:33:46 bytserver zfs: Try running '/sbin/modprobe zfs' as root to load them.
Feb 19 13:33:46 bytserver systemd: zfs-share.service: Main process exited, code=exited, status=1/FAILURE
Feb 19 13:33:46 bytserver systemd: zfs-share.service: Failed with result 'exit-code'.
Feb 19 13:33:46 bytserver systemd: Failed to start ZFS file system shares.
Feb 19 13:33:46 bytserver systemd: Reached target ZFS startup target.
Feb 19 13:33:47 bytserver containerd: time="2021-02-19T13:33:47.608958319+01:00" level=info msg="loading plugin \"io.containerd.snapshotter.v1.zfs\"..." type=io.containerd.snapshotter.v1
Feb 19 13:33:47 bytserver containerd: time="2021-02-19T13:33:47.609214490+01:00" level=info msg="skip loading plugin \"io.containerd.snapshotter.v1.zfs\"..." error="path /var/lib/containerd/io.containerd.snapshotter.v1.zfs must be a zfs filesystem to be used with the zfs snapshotter: skip plugin" type=io.containerd.snapshotter.v1
Feb 19 14:27:39 bytserver sudo:     john : TTY=pts/1 ; PWD=/dev/disk/by-label ; USER=root ; COMMAND=/usr/bin/apt install zfs
Feb 19 14:27:53 bytserver sudo:     john : TTY=pts/1 ; PWD=/dev/disk/by-label ; USER=root ; COMMAND=/usr/bin/apt install zfs
Feb 19 14:30:58 bytserver sudo:     john : TTY=pts/1 ; PWD=/dev/disk/by-label ; USER=root ; COMMAND=/usr/bin/apt-get install zfs-dkms
Feb 19 14:31:21 bytserver sudo:     john : TTY=pts/1 ; PWD=/dev/disk/by-label ; USER=root ; COMMAND=/usr/sbin/modprobe zfs
Feb 19 14:31:29 bytserver sudo:     john : TTY=pts/1 ; PWD=/dev/disk/by-label ; USER=root ; COMMAND=/usr/bin/apt install zfs
Feb 19 14:34:21 bytserver sudo:     john : TTY=pts/1 ; PWD=/dev/disk/by-label ; USER=root ; COMMAND=/usr/bin/add-apt-repository ppa:zfs-native/stable
Feb 19 14:52:35 bytserver sudo:     john : TTY=pts/1 ; PWD=/home/john/openzfs-docs ; USER=root ; COMMAND=/usr/bin/vi /etc/apt/sources.list
Feb 19 14:53:47 bytserver sudo:     john : TTY=pts/1 ; PWD=/home/john/openzfs-docs ; USER=root ; COMMAND=/usr/bin/apt update
Feb 19 14:53:59 bytserver sudo:     john : TTY=pts/1 ; PWD=/home/john/openzfs-docs ; USER=root ; COMMAND=/usr/bin/vi /etc/apt/sources.list
Feb 19 14:54:08 bytserver sudo:     john : TTY=pts/1 ; PWD=/home/john/openzfs-docs ; USER=root ; COMMAND=/usr/bin/apt update
Feb 19 14:54:54 bytserver sudo:     john : TTY=pts/1 ; PWD=/home/john/openzfs-docs ; USER=root ; COMMAND=/usr/bin/su
Feb 19 14:56:22 bytserver sudo:     root : TTY=pts/1 ; PWD=/home/john/openzfs-docs ; USER=root ; COMMAND=/usr/bin/apt upgrade
Feb 19 14:56:59 bytserver sudo:    john : TTY=pts/1 ; PWD=/home/john/openzfs-docs ; USER=root ; COMMAND=/usr/bin/apt install --yes -t buster-backports --no-install-recommends zfs-dkms
Feb 19 14:57:20 bytserver sudo:     john : TTY=pts/1 ; PWD=/home/john/openzfs-docs ; USER=root ; COMMAND=/usr/bin/apt install --yes -t buster-backports zfsutils-linux
Feb 19 14:57:39 bytserver sudo:     john : TTY=pts/1 ; PWD=/home/john/openzfs-docs ; USER=root ; COMMAND=/usr/bin/apt install --yes mdadm
Feb 19 15:03:10 bytserver sudo:     john : TTY=pts/1 ; PWD=/home/john ; USER=root ; COMMAND=/usr/bin/apt install -t buster-backports zfsutils-linux
Feb 19 15:03:23 bytserver sudo:     john : TTY=pts/1 ; PWD=/home/john ; USER=root ; COMMAND=/usr/bin/apt install -t buster-backports zfsutils-linu
Feb 19 15:03:33 bytserver sudo:     john : TTY=pts/1 ; PWD=/home/john ; USER=root ; COMMAND=/usr/bin/apt install zfs-dkms
Feb 19 15:05:36 bytserver systemd-udevd: Process '/sbin/modprobe zfs' failed with exit code 1.
Feb 19 15:07:20 bytserver systemd-udevd: Process '/sbin/modprobe zfs' failed with exit code 1.
Feb 19 15:10:51 bytserver sudo:     john : TTY=pts/1 ; PWD=/home/john ; USER=root ; COMMAND=/usr/bin/apt-get -y install zfs-dkms
Feb 19 15:11:58 bytserver sudo:     john : TTY=pts/1 ; PWD=/home/john ; USER=root ; COMMAND=/usr/bin/systemctl restart zfs-import-cache
Feb 19 15:11:58 bytserver systemd: Starting Install ZFS kernel module...
Feb 19 15:11:58 bytserver modprobe: modprobe: FATAL: Module zfs not found in directory /lib/modules/4.19.0-14-amd64
Feb 19 15:11:58 bytserver systemd: zfs-load-module.service: Main process exited, code=exited, status=1/FAILURE
Feb 19 15:11:58 bytserver systemd: zfs-load-module.service: Failed with result 'exit-code'.
Feb 19 15:11:58 bytserver systemd: Failed to start Install ZFS kernel module.
Feb 19 15:11:58 bytserver systemd: Dependency failed for Import ZFS pools by cache file.
Feb 19 15:11:58 bytserver systemd: zfs-import-cache.service: Job zfs-import-cache.service/start failed with result 'dependency'.
Feb 19 15:15:56 bytserver sudo:     john : TTY=pts/1 ; PWD=/home/john ; USER=root ; COMMAND=/usr/bin/apt-get install zfsutils-linux

What could I do diagnoze and to fix it? Thank you for help