Touchpad switch not working (Lenovo IdeaPad, Kubuntu 20.04)

Do you have the latest BIOS?

I suppose it is, I do updates. How do I check?

Manufacturers website. It may need Windows but some can access FAT32 formatted USB and you can do it that way

there seems lot of new "touchpad not working / not found" bugs:
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1884997
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1884981
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1883905
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1882850

Ah, that question is only for on/off switch not working.

Does xev report event when you press that button? It probably should report XF86TouchpadToggle event. Or does something
printed to dmesg/logs when you press that button?

https://wiki.ubuntu.com/DebuggingTouchpadDetection/xev

- I believe Lenovo pushes its BIOS updates through Windows Update (it publishes at least some updates), and I've just updated my Win10;
- xev does not report anything when I press Fn-F6 (though it does when I press F6, or Fn-F5, or Fn-F7)
- dmesg does not print any error linked with me pressing Fn-F6

Oh, yeah, just checked the bugs you linked. My touchpad works well when activated through the usual settings.

In fact, I did not have the latest BIOS. Now I do, and the issue remains the same.

Is "Ideapad extra buttons" listed on /proc/bus/input/devices (or xinput --list)? And all other special keys works?

I guess that button should be handled ideapad_laptop driver. Driver has some debugfs-files that may be give some hint.
https://cateee.net/lkddb/web-lkddb/IDEAPAD_LAPTOP.html
https://github.com/torvalds/linux/blob/master/drivers/platform/x86/ideapad-laptop.c

and your hardware is something like:
https://linux-hardware.org/index.php?probe=50c621a5c6

"Ideapad extra buttons" is listed, both in /proc/bus/input/devices and in xinput --list
All other special keys do work

I don't know how to interpret the links you gave me

What file /sys/devices/platform/ideapad/touchpad tells you? It should be 1 when touchpad is switched on and 0 when its off.

I do not have the same directory tree as you suggest.

The only file named "touchpad" in /sys is 1, whatever the (kubuntu) setting for touchpad is.
The file is located in /sys/devices/pci0000:00/0000:00:1f.0/PNP0C09:00/VPC2004:00/touchpad

That file and directory is probably correct one (and kernel documentation misleading [1]). Does the file change when you press button?

File /sys/kernel/debug/ideapad/status [2] should tell status.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/ABI/testing/sysfs-platform-ideapad-laptop
[2] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/ABI/testing/debugfs-ideapad

Neither the file /sys/devices/pci0000:00/0000:00:1f.0/PNP0C09:00/VPC2004:00/touchpad nor /sys/kernel/debug/ideapad/status (this one exists) are modified by either Fn-F6 or changing the setting through Kubuntu Settings.

BTW, /sys/kernel/debug/ideapad/status indicates that my Wi-Fi is off, while it is on, and does not reflect changes of "backlight".

I suggest you report bug...

Bug reported here https://bugs.launchpad.net/ubuntu/+bug/1885033

https://wiki.ubuntu.com/Kernel/Bugs#Adding_debug_info_to_a_bug_report

Should I file the bug against "linux"?

yes

This is probably good to mention directly on bug report:
"Neither the file /sys/devices/pci0000:00/0000:00:1f.0/PNP0C09:00/VPC2004:00/touchpad nor /sys/kernel/debug/ideapad/status (this one exists) are modified by either Fn-F6 or changing the setting through Kubuntu Settings"

oh, we also missed at least one step:
"if the key code is wrong, or there is no keypress event, or the key only works once and then the desktop gets "stuck", install the "evtest" package, run sudo evtest, select your keyboard device, press the broken keys, and note down their scan code (MSC_SCAN), current keycode (KEY_*), and intended meaning. "

https://wiki.ubuntu.com/Hotkeys/Troubleshooting

For this step, I think I should write what happens for every special key:
F1 through F12 show the corresponding keycode.
On its own, Fn does not appear at all.
Fn-F1 (mute) shows MSC_SCAN value a0, keycode 113 (KEY_MUTE) with values alternating 1-0 (as I press/release, this will be the same)
Fn-F2 (vol down) and Fn-F3 (vol up) show MSC_SCAN values ae and b0, with keycodes 114 (KEY_VOLUMEDOWN) and 114 (KEY_VOLUMEUP)
Fn-F4 (mute mic) does not appear at all (it works well though)
Fn-F5 (reload) appears as F5
Fn-F6 (touchpad switch) does not appear at all (and doesn't work)
Fn-F7 (airplane mode) does not appear at all (but works)
Fn-F8 (cut camera, I guess?) does not appear at all (doesn't work? I haven't found its use, but when streaming my webcam to VLC, it did nothing)
Fn-F9 (lock) appears as LEFTMETA-L, where releasing F9 releases L and Fn releases LEFTMETA
Fn-F10 (change multiscreen options) appears as LEFTMETA-P where repressing F10 represses P and releasing Fn releases LEFTMETA
Fn-F11 (luminosity down) and Fn-F12 (luminosity up) do not appear at all (but work well though)

How long do you think this will take before this bug is resolved?

I don't know, but bug probably falls to "if there is neither an ACPI event nor an input event, this is probably also a kernel bug, though probably harder to diagnose" category, so i may take some time (months, years).

I have no idea what nexts. Maybe something related to acpi and kernel, like:
https://ubuntu.com/blog/debug-dsdt-ssdt-with-acpica-utilities

My query lies inside the realm of technical vulnerability detection, no longer from the distro utilization attitude. I am doing a research on diverse field image scanners and need a manner to determine whether vulnerabilities flagged through scanners are TPs of FPs. Find best guides on the website https://www.unique-links.com.pk/web-hosting/ I can do this pretty smooth on LTS releases but looking for a reliable way to do that on semi-annual releases.

I think you wanted to open a new question (https://answers.launchpad.net/ubuntu/+addquestion) instead of commenting on this one, as I see no link between "technical vulnerability detection" and "diverse field image scanners" and my original question about a keybinding not working.