I have not tried the procedure from the original post. Instead, I added the following configuration file and rebooted. I would suggest it instead. The documentation is available in man zram-generator.conf.
$ cat /etc/systemd/zram-generator.conf.d/librem5.conf
[zram0]
zram-fraction = 2
max-zram-size = none
That configuration file overrides the configuration file with the same name, which is provided by Purism.
$ cat /usr/lib/systemd/zram-generator.conf.d/librem5.conf
[zram0]
So, this combines the following advice.