"sort" from coreutils block root for a long time (3min) at boot; what is this in Debian11 64bits?

At boot, I see the process
Quote:

/usr/bin/sort -z

running which block my apt-get upgrade
sort is from coreutils and is version 8.32-4+b1

my system is a Debian Gnome 64bits
uname -v
Quote:

#1 SMP Debian 5.10.205-2 (2023-12-31)

Any idea why this sort must run and what it does? Any hint is welcome (no urgency: the PC works)

Sort is described there https://www.gnu.org/software/coreuti...ort-invocation
Quote:

i-zi i--zero-terminatedi Delimit items with a zero byte rather than a newline (ASCII LF). I.e., treat input as items separated by ASCII NUL and terminate output items with ASCII NUL. This option can be useful in conjunction with iperl -0i or ifind -print0i and ixargs -0i which do the same in order to reliably handle arbitrary file names (even those containing blanks or other special characters).