Comment 1 for bug 1938104

Why is this invalid? I presume because there's the idmapped mounts feature. The problem is that this doesn't work in 5.13 when BTRFS is the underlying filesystem. So shiftfs is still useful. Its turned on in master build[1], why not for OEM, which is the only 5.13 available for focal?

Here's a discussion suggesting that idmapped mounts for BTRFS won't be available till 5.15[2]

[1] https://git.launchpad.net/~canonical-kernel/ubuntu/+source/linux-oem/+git/focal/commit/?h=oem-5.13&id=c79066e1cb62dee340b050e98284939bcdabef0f
[2] https://discuss.linuxcontainers.org/t/are-there-plans-to-map-shiftfs-config-option-to-new-5-12-kernel-id-mapping/11704/5?u=crass