Try this:
systemctl start systemd-zram-setup@zram0.service
and then check the status:
systemctl status systemd-zram-setup@zram0.service
With this and the minimal config it has already worked that zram0 is shown up.
That with …sudo systemctl start /dev/zram0… I had from this forum post.
have then now tried line by line to test the config from my first post. But as soon as I enter one following lines* zram0 is gone again. So here seems to be a problem.
I had the lines from the example config “zram-generator.conf.example” and from https://github.com/systemd/zram-generator/blob/main/README.md
*fs-type = btrfs
mount-point = /var/compressed
options = X-mount.mode=1777