Hi, jazzbiker. I repeated the xev and showkey experiments after booting TCL with the atkbd.softraw=0 kernel boot paramter. Alas, no difference. Here is what dmesg says about my keyboard:
TCL$ dmesg | grep keyboard
input: AT Translated Set 2 keyboard as /devices/platform/i8042/serio0/input/input3
Rich, no exact matches among the packages installed on Devuan:
Devuan$ apt list --installed | grep -E 'key|map|input|udev|device'
WARNING: apt does not have a stable CLI interface. Use with caution in scripts.
debian-archive-keyring/stable,now 2017.5 all [installed]
devuan-keyring/stable,now 2017.10.03 all [installed]
eudev/stable,now 3.2.2-13 amd64 [installed]
gir1.2-gnomekeyring-1.0/stable,now 3.12.0-1+b2 amd64 [installed,automatic]
gir1.2-gudev-1.0/stable,now 230-3 amd64 [installed,automatic]
gnome-keyring/stable,now 3.20.0-3 amd64 [installed]
keyboard-configuration/stable,now 1.164 all [installed]
keyutils/stable,now 1.5.9-9 amd64 [installed,automatic]
libavdevice-dev/stable,now 7:3.2.10-1~deb9u1 amd64 [installed]
libavdevice57/stable,now 7:3.2.10-1~deb9u1 amd64 [installed,automatic]
libchromaprint1/stable,now 1.4.2-1 amd64 [installed,automatic]
libdevmapper1.02.1/stable,now 2:1.02.137-2 amd64 [installed,automatic]
libdmapsharing-3.0-2/stable,now 2.9.37-1 amd64 [installed,automatic]
libeudev-dev/stable,now 3.2.2-13 amd64 [installed,automatic]
libeudev1/stable,now 3.2.2-13 amd64 [installed,automatic]
libgnome-keyring-common/stable,now 3.12.0-1 all [installed,automatic]
libgnome-keyring0/stable,now 3.12.0-1+b2 amd64 [installed,automatic]
libgudev-1.0-0/stable,now 230-3 amd64 [installed,automatic]
libgudev-1.0-dev/stable,now 230-3 amd64 [installed]
libimobiledevice6/stable,now 1.2.0+dfsg-3.1 amd64 [installed,automatic]
libinput-bin/stable,now 1.6.3-1 amd64 [installed,automatic]
libinput10/stable,now 1.6.3-1 amd64 [installed,automatic]
libkeyutils1/stable,now 1.5.9-9 amd64 [installed,automatic]
libnfsidmap2/stable,now 0.25-5.1 amd64 [installed,automatic]
libpam-gnome-keyring/stable,now 3.20.0-3 amd64 [installed,automatic]
libudev-dev/stable,now 1:3.2.2+devuan2.11 amd64 [installed,automatic]
libudev1/stable,now 1:3.2.2+devuan2.11 amd64 [installed]
libwinpr-input0.1/stable,now 1.1.0~git20140921.1.440916e+dfsg1-13+deb9u2 amd64 [installed,automatic]
libxcb-keysyms1/stable,now 0.4.0-1+b2 amd64 [installed,automatic]
nmap/stable,now 7.40-1 amd64 [installed]
python-keyring/stable,now 10.1-1 all [installed,automatic]
python-keyrings.alt/stable,now 1.3-1 all [installed,automatic]
python3-keyring/stable,now 10.1-1 all [installed,automatic]
python3-keyrings.alt/stable,now 1.3-1 all [installed,automatic]
system-config-printer-udev/stable,now 1.5.7-3+b1 amd64 [installed,automatic]
udev/stable,now 1:3.2.2+devuan2.11 amd64 [installed]
x11proto-input-dev/stable,now 2.3.2-1 all [installed,automatic]
xbitmaps/stable,now 1.1.1-2 all [installed,automatic]
xinput/stable,now 1.6.2-1+b1 amd64 [installed]
xserver-xorg-input-all/stable,now 1:7.7+19 amd64 [installed,automatic]
xserver-xorg-input-libinput/stable,now 0.23.0-2 amd64 [installed,automatic]
xserver-xorg-input-synaptics/stable,now 1.9.0-1+b1 amd64 [installed]
xserver-xorg-input-void/stable,now 1:1.4.1-1+b2 amd64 [installed,automatic]
xserver-xorg-input-wacom/stable,now 0.34.0-1 amd64 [installed,automatic]
The xserver-* packages are probably unrelated, since the Fn+F4 key works just fine in console when X is not running.