https://extensions.gnome.org/extension/3939/fnlock-switch-thinkpad-compact-usb-keyboard/

fnlock-switch

GNOME shell extension that adds FnLock toggle button (indicator) to GNOME top panel. Supports both:

• Lenovo ThinkPad Compact USB Keyboard
• Lenovo ThinkPad Trackpoint Keyboard II (wireless / Bluetooth)

FnLock is active (locked)

FnLock is inactive (unlocked)

FnLock not found

Configuration

It needs write access to /sys/.../fn_lock, and /dev/fnlock-switch symlink must exist. An example udev rule:

cat <<'EOF' >  /etc/udev/rules.d/99-thinkpad-keyboard.rules
SUBSYSTEM=="input", DRIVERS=="lenovo", RUN += "/bin/sh -c 'FILE=$(find /sys/devices/ -name fn_lock 2>/dev/null); test -f $FILE && chown <CHANGE_USERNAME> $FILE && ln -f -s $FILE /dev/fnlock-switch'"
EOF

Keybinding

Extension's keybinding for both keyboards is Ctrl  + Esc 
It looks like there is no way to bind Fn button for keybindings, so Ctrl here is fine too.

The stadard hardware keybinding on wireless keyboard in Bluetooth mode will work as well: Fn  + Esc 

Custom keybinding

TBD: prefs

# workaround
cat << EOF | dconf load /org/gnome/shell/extensions/fnlock/
[/]
keybinding=['<Control>Escape']
EOF

Why?

1. FnLock current status indicator seems to be helpful
2. Solution for isssue with ThinkPad Compact USB Keyboard and Lenovo ThinkPad Trackpoint Keyboard II (2.4G wireless mode), when Fn+Esc isn't working in Linux. Manual toggling by writing 1|0 into /sys/.../fn_lock is possible though.

☕

If you like this GNOME extension, you may buy me a coffee sometime
https://www.donationalerts.com/r/dmitry_goloshubov