Clickpad left click not working on Ubuntu 20.04 when touchpad is not touched

I have a problem with a new Ubuntu 20.04 setup on a new computer (Dell Precision 7550). The clickpad/touchpad looks like the following:

The right and middle buttons work all the time. However the left button only works when the touchpad is being touched which is very annoying.

Question: how to fix the problem and make the left button of the clickpad work even when the touchpad is not being touched?

Here is the current configuration. The following packages are installed on my computer:

• libinput-bin 1.15.5-1
• libinput10 1.15.5-1
• xserver-xorg-input-libinput 0.29.0-1
• xserver-xorg-input-synaptics 1.9.1-1

Here is what I get when I print xinput list:

⎡ Virtual core pointer                      id=2    [master pointer  (3)]
⎜   ↳ Virtual core XTEST pointer                id=4    [slave  pointer  (2)]
⎜   ↳ DELL09C3:00 0488:120A Mouse               id=11   [slave  pointer  (2)]
⎜   ↳ DELL09C3:00 0488:120A Touchpad            id=12   [slave  pointer  (2)]
⎜   ↳ PS/2 Generic Mouse                        id=18   [slave  pointer  (2)]
⎣ Virtual core keyboard                     id=3    [master keyboard (2)]
    ↳ Virtual core XTEST keyboard               id=5    [slave  keyboard (3)]
    ↳ Video Bus                                 id=6    [slave  keyboard (3)]
    ↳ Power Button                              id=7    [slave  keyboard (3)]
    ↳ Sleep Button                              id=8    [slave  keyboard (3)]
    ↳ Integrated_Webcam_HD: Integrate           id=10   [slave  keyboard (3)]
    ↳ DELL09C3:00 0488:120A UNKNOWN             id=13   [slave  keyboard (3)]
    ↳ Intel HID events                          id=14   [slave  keyboard (3)]
    ↳ Intel HID 5 button array                  id=15   [slave  keyboard (3)]
    ↳ Dell WMI hotkeys                          id=16   [slave  keyboard (3)]
    ↳ AT Translated Set 2 keyboard              id=17   [slave  keyboard (3)]

Here is the content of the file /usr/share/X11/xorg.conf.d/40-libinput.conf:

# Match on all types of devices but joysticks
#
# If you want to configure your devices, do not copy this file.
# Instead, use a config snippet that contains something like this:
#
# Section "InputClass"
#   Identifier "something or other"
#   MatchDriver "libinput"
#
#   MatchIsTouchpad "on"
#   ... other Match directives ...
#   Option "someoption" "value"
# EndSection
#
# This applies the option any libinput device also matched by the other
# directives. See the xorg.conf(5) man page for more info on
# matching devices.

Section "InputClass"
        Identifier "libinput pointer catchall"
        MatchIsPointer "on"
        MatchDevicePath "/dev/input/event*"
        Driver "libinput"
EndSection

Section "InputClass"
        Identifier "libinput keyboard catchall"
        MatchIsKeyboard "on"
        MatchDevicePath "/dev/input/event*"
        Driver "libinput"
EndSection

Section "InputClass"
        Identifier "libinput touchpad catchall"
        MatchIsTouchpad "on"
        MatchDevicePath "/dev/input/event*"
        Driver "libinput"
EndSection

Section "InputClass"
        Identifier "libinput touchscreen catchall"
        MatchIsTouchscreen "on"
        MatchDevicePath "/dev/input/event*"
        Driver "libinput"
EndSection

Section "InputClass"
        Identifier "libinput tablet catchall"
        MatchIsTablet "on"
        MatchDevicePath "/dev/input/event*"
        Driver "libinput"
EndSection

and the content of usr/share/X11/xorg.conf.d/51-synaptics-quirks.conf:

Section "InputClass"
    Identifier "Dell Inspiron embedded buttons quirks"
    MatchTag "inspiron_1011|inspiron_1012"
    MatchDevicePath "/dev/input/event*"
    Driver "synaptics"
    Option "JumpyCursorThreshold" "90"
EndSection

Section "InputClass"
    Identifier "Dell Inspiron quirks"
    MatchTag "inspiron_1120"
    MatchDevicePath "/dev/input/event*"
    Driver "synaptics"
    Option "JumpyCursorThreshold" "250"
EndSection

Section "InputClass"
    Identifier "HP Mininote quirks"
    MatchTag "mininote_1000"
    MatchDevicePath "/dev/input/event*"
    Driver "synaptics"
    Option "JumpyCursorThreshold" "20"
EndSection

and the content of /usr/share/X11/xorg.conf.d/70-synaptics.conf:

# Example xorg.conf.d snippet that assigns the touchpad driver
# to all touchpads. See xorg.conf.d(5) for more information on
# InputClass.
# DO NOT EDIT THIS FILE, your distribution will likely overwrite
# it when updating. Copy (and rename) this file into
# /etc/X11/xorg.conf.d first.
# Additional options may be added in the form of
#   Option "OptionName" "value"
#
Section "InputClass"
        Identifier "touchpad catchall"
        Driver "synaptics"
        MatchIsTouchpad "on"
# This option is recommend on all Linux systems using evdev, but cannot be
# enabled by default. See the following link for details:
# http://who-t.blogspot.com/2010/11/how-to-ignore-configuration-errors.html
      MatchDevicePath "/dev/input/event*"
EndSection

Section "InputClass"
        Identifier "touchpad ignore duplicates"
        MatchIsTouchpad "on"
        MatchOS "Linux"
        MatchDevicePath "/dev/input/mouse*"
        Option "Ignore" "on"
EndSection

# This option enables the bottom right corner to be a right button on clickpads
# and the right and middle top areas to be right / middle buttons on clickpads
# with a top button area.
# This option is only interpreted by clickpads.
Section "InputClass"
        Identifier "Default clickpad buttons"
        MatchDriver "synaptics"
        Option "SoftButtonAreas" "50% 0 82% 0 0 0 0 0"
        Option "SecondarySoftButtonAreas" "58% 0 0 15% 42% 58% 0 15%"
EndSection

# This option disables software buttons on Apple touchpads.
# This option is only interpreted by clickpads.
Section "InputClass"
        Identifier "Disable clickpad buttons on Apple touchpads"
        MatchProduct "Apple|bcm5974"
        MatchDriver "synaptics"
        Option "SoftButtonAreas" "0 0 0 0 0 0 0 0"
EndSection