The ID-mapped mounts feature was added to
Linux in 5.12, but the general idea behind it goes back a fair bit
further. There are a number of different situations where the user and
group IDs for files on disk do not match the current human (or process) user of those
files, so ID-mapped mounts provide a way to resolve that problem—without
changing the files on disk. The developer of the feature, Christian
Brauner, led a discussion at the
2022 Linux Storage,
Filesystem, Memory-management and BPF Summit (LSFMM) on ID-mapped mounts.

Source: LWN.net – [$] ID-mapped mounts