The issue came from a device which was not properly mounted.

strace was hanging here:

[...]
getcwd("/home/myself/build-mountedvolumes-Desktop-Debug", 4096) = 50
lstat("/home/myself/build-mountedvolumes-Desktop-Debug/systemd-1", 0x7ffcc45c5d70) = -1 ENOENT (No such file or directory)
open("/dev/disk/by-label", O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
read(3, "nproto=5,maxproto=5,direct\n93 20"..., 1024) = 1024
lstat("/home", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
lstat("/home/user", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
lstat("/home/user/SSD211", {st_mode=S_IFDIR|0755, st_size=0, ...}) = 0
open("/proc/self/mountinfo", O_RDONLY|O_CLOEXEC) = 4
fstat(4, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0
read(4, "18 24 0:17 / /sys rw,nosuid,node"..., 1024) = 1024
read(4, "s-agent,name=systemd\n30 18 0:24 "..., 1024) = 1024
read(4, "oexec,relatime shared:21 - cgrou"..., 1024) = 1024
read(4, "nproto=5,maxproto=5,direct\n93 20"..., 1024) = 1024
read(4, "user/SSD212 rw,relatime share"..., 1024) = 536
read(4, "", 1024)                       = 0
close(4)                                = 0
statfs("/home/user/SSD211", ^C

This happened because [Automount] and [Mount] directives in our systemd services failed but left the device in a unstable state. Or maybe that the service was just hanging and no releasing the device while trying to mount it, preventing QStorageInfo::mountedVolumes() to access the device.

Thanks again for your help!

strace ./your_app

and put the output here - maybe we can see where exactly it is hanging.

.1 has over 300 bug fixes, maybe this is one of them.