The admin backend is broken

Thank you for taking the time to report this bug and helping to make Ubuntu better. It sounds like some part of the system has crashed. To help us find the cause of the crash please follow these steps:

1. Look in /var/crash for crash files and if found run:
    ubuntu-bug YOURFILE.crash
Then tell us the ID of the newly-created bug.

2. If step 1 failed then look at https://errors.ubuntu.com/user/ID where ID is the content of file /var/lib/whoopsie/whoopsie-id on the machine. Do you find any links to recent problems on that page? If so then please send the links to us.

3. If step 2 also failed then apply the workaround from bug 994921, reboot, reproduce the crash, and retry step 1.

Please take care to avoid attaching .crash files to bugs as we are unable to process them as file attachments. It would also be a security risk for yourself.

my /var/crash is empty
https://errors.ubuntu.com/user/39229ebea988d6578bed98d7e18bd96fd9cd523cf89495ed70d4ce4c0f8b7937667368f389be8d8b2588bafc31d1935109305b4abf52dbb724a7cf43c3b425b4

my /etc/apport/crashdb.conf is as follows and I don't see a line like:
line 23 ("'problem_types': ['Bug', 'Package'],") in '/etc/apport/crashdb.conf'.

corrado@corrado-n2-hh-0402:~$ cat /etc/apport/crashdb.conf
# map crash database names to CrashDatabase implementations and URLs

default = 'ubuntu'

def get_oem_project():
    '''Determine OEM project name from Distribution Channel Descriptor

    Return None if it cannot be determined or does not exist.
    '''
    try:
        dcd = open('/var/lib/ubuntu_dist_channel').read()
        if dcd.startswith('canonical-oem-'):
            return dcd.split('-')[2]
    except IOError:
        return None

databases = {
    'ubuntu': {
        'impl': 'launchpad',
        'bug_pattern_url': 'http://people.canonical.com/~ubuntu-archive/bugpatterns/bugpatterns.xml',
        'dupdb_url': 'http://people.canonical.com/~ubuntu-archive/apport-duplicates',
        'distro': 'ubuntu',
        'escalation_tag': 'bugpattern-needed',
        'escalated_tag': 'bugpattern-written',
    },
    'canonical-oem': {
        'impl': 'launchpad',
        'bug_pattern_url': 'http://people.canonical.com/~ubuntu-archive/bugpatterns/bugpatterns.xml',
        'project': get_oem_project(),
    },
    'debug': {
        # for debugging
        'impl': 'memory',
        'bug_pattern_url': '/tmp/bugpatterns.xml',
        'distro': 'debug'
    },
}
corrado@corrado-n2-hh-0402:~$

now I will reboot, reproduce problem and try to find trace of the problem in journal

If it's the same crash your nautilus had on Feb 22 then it would be bug 1627564.

Attached journal with the problem.
problem occurred at line 2726 apr 06 08:32:16
where you see the password request to access the other home

I don't know what that is but maybe it should be reported at: https://gitlab.freedesktop.org/groups/polkit/-/issues

Problem is described in:
https://gitlab.freedesktop.org/polkit/polkit/-/issues/136
to try:
corrado@corrado-n2-hh-0402:~$ gedit admin:///home

(gedit:12489): GVFS-WARNING **: 17:49:21.210: The peer-to-peer connection failed: Could not connect: Permission denied. Falling back to the session bus. Your application is probably missing --filesystem=xdg-run/gvfsd privileges.

** (gedit:12489): WARNING **: 17:49:21.219: Hit unhandled case 36 (GDBus.Error:org.freedesktop.PolicyKit1.Error.Failed: Unix process subject does not have uid set) in parse_error.
corrado@corrado-n2-hh-0402:~$

Could not open the file “admin:///home”.
Unexpected error: GDBus.Error:org.freedesktop.PolicyKit1.Error.Failed: Unix process subject does not have uid set

Seems it was broken due to the changes in https://gitlab.gnome.org/GNOME/gvfs/-/issues/515

Status changed to 'Confirmed' because the bug affects multiple users.

The issue is fixed in upstream git https://gitlab.gnome.org/GNOME/gvfs/-/merge_requests/122/

Still having the problem in Ubuntu 21.04 gedit: Installed: 3.38.1-1

Still same problem
corrado@corrado-n4-ii-0718:~$ inxi -Fx
System: Host: corrado-n4-ii-0718 Kernel: 5.11.0-20-generic x86_64 bits: 64 compiler: gcc v: 10.2.1 Desktop: GNOME 40.2
           Distro: Ubuntu 21.10 (Impish Indri)
Machine: Type: Laptop System: Dell product: Inspiron 3793 v: N/A serial: <superuser required>
           Mobo: Dell model: 0C1PF2 v: A00 serial: <superuser required> UEFI: Dell v: 1.5.0 date: 12/17/2019
Battery: ID-1: BAT0 charge: 38.3 Wh condition: 38.3/42.0 Wh (91%) model: SWD-ATL3.618 DELL WJPC403 status: Full
CPU: Info: Quad Core model: Intel Core i5-1035G1 bits: 64 type: MT MCP arch: Ice Lake rev: 5 L2 cache: 6 MiB
           flags: avx avx2 lm nx pae sse sse2 sse3 sse4_1 sse4_2 ssse3 vmx bogomips: 19046
           Speed: 1000 MHz min/max: 400/1000 MHz Core speeds (MHz): 1: 1000 2: 976 3: 933 4: 929 5: 978 6: 910 7: 805 8: 916
Graphics: Device-1: Intel Iris Plus Graphics G1 vendor: Dell driver: i915 v: kernel bus ID: 00:02.0
           Device-2: Realtek Integrated_Webcam_HD type: USB driver: uvcvideo bus ID: 1-6:3
           Display: wayland server: X.Org 1.21.1.1 compositor: gnome-shell driver: loaded: i915
           note: n/a (using device driver) resolution: 1920x1080~60Hz
           OpenGL: renderer: Mesa Intel UHD Graphics (ICL GT1) v: 4.6 Mesa 21.1.4 direct render: Yes
Audio: Device-1: Intel Ice Lake-LP Smart Sound Audio vendor: Dell driver: snd_hda_intel v: kernel bus ID: 00:1f.3
           Sound Server: ALSA v: k5.11.0-20-generic
Network: Device-1: Realtek RTL810xE PCI Express Fast Ethernet vendor: Dell driver: r8169 v: kernel port: 3000
           bus ID: 01:00.0
           IF: enp1s0 state: down mac: 98:e7:43:59:19:19
           Device-2: Qualcomm Atheros QCA9377 802.11ac Wireless Network Adapter vendor: Dell driver: ath10k_pci v: kernel
           port: 3000 bus ID: 02:00.0
           IF: wlp2s0 state: up mac: d8:12:65:b8:21:b9
           Device-3: Qualcomm Atheros type: USB driver: btusb bus ID: 1-10:4
Bluetooth: Device-1: Qualcomm Atheros type: USB driver: btusb v: 0.8 bus ID: 1-10:4
           Report: ID: hci0 state: up running bt-v: 2.1 lmp-v: 4.2 address: D8:12:65:B8:21:BA
Drives: Local Storage: total: 942.7 GiB used: 11.9 GiB (1.3%)
           ID-1: /dev/nvme0n1 vendor: Toshiba model: KBG40ZNS512G NVMe KIOXIA 512GB size: 476.94 GiB temp: 31.9 C
           ID-2: /dev/sda vendor: Crucial model: CT500MX500SSD1 size: 465.76 GiB
Partition: ID-1: / size: 31.2 GiB used: 11.43 GiB (36.6%) fs: ext4 dev: /dev/nvme0n1p4
           ID-2: /boot/efi size: 246 MiB used: 46.4 MiB (18.9%) fs: vfat dev: /dev/nvme0n1p1
Swap: ID-1: swap-1 type: partition size: 8 GiB used: 0 KiB (0.0%) dev: /dev/nvme0n1p2
Sensors: System Temperatures: cpu: 53.0 C mobo: N/A
           Fan Speeds (RPM): cpu: 0
Info: Processes: 261 Uptime: 2h 05m Memory: 7.54 GiB used: 4.4 GiB (58.3%) Init: systemd runlevel: 5 Compilers: gcc: N/A
           Packages: 1835 Shell: Bash v: 5.1.8 inxi: 3.3.01
corrado@corrado-n4-ii-0718:~$

Problem is fixed by Latest upstream version 1.48.1. but in Ubuntu I still have 1.47.91-1ubuntu1
see https://gitlab.gnome.org/GNOME/gvfs/-/merge_requests/122

Still waiting for latest upstream version.

fixed in jammy by
corrado@corrado-jj-1023:~$ apt policy gvfs
gvfs:
  Installed: 1.48.1-2ubuntu2
  Candidate: 1.48.1-2ubuntu2
  Version table:
 *** 1.48.1-2ubuntu2 500
        500 http://archive.ubuntu.com/ubuntu jammy/main amd64 Packages
        100 /var/lib/dpkg/status
corrado@corrado-jj-1023:~$