Comment 3 for bug 1925989

There is a new way of managing zram using zram-config in Ubuntu 22.04: instead of use X devices (one per cpu-core) it uses only one device with X streams associated (one stream per cpu-core).

Run zramctl command: you can see that there is only one device but with X streams associated.

There is a brief annotation in raspi-config changelog for 0.7 version (link: https://launchpad.net/ubuntu/+source/zram-config/+changelog):

zram-config (0.7) jammy; urgency=medium

  * Only setup a single zram device, multiple devices have not been
    needed since kernel 3.15

Well, I don't know if there is a typo; it says kernel 3.15 but may be kernel 5.15 (?).

But as you said, having only 256MB associated to a zram device in a 64GB RAM machine is strange.