QEMU USB Tablet is not detected by XOrg on arm64

[Compilebunny]

I am attempting to run Alpine Linux 3.15 in qemu-system-aarch64 on
Raspberry Pi. The Raspberry Pi is set up with a touchscreen and acts like
a tablet.

The problem is that I do not get any mouse action on the graphical console
when I run startx on the guest. Xorg loads, but there is no mouse. While
"dmesg | grep 1-2" suggests that "QEMU USB Tablet" has been detected and
given a place in /dev/input, Xorg does not detect it.

/usr/share/X11/xorg.conf.d/40-libinput.conf is set up to identify various
classes of input devices using "MatchIsTablet", "MatchIsTouchscreen", etc.

Unfortunately, it never identifies QEMU USB Tablet and therefore XOrg does
not get a pointer.

The host OS is Ubuntu Mate 20.04.3 LTS. This is the most recent long term
support version of Ubuntu. Setup was performed using virt-manager.

Host software versions:
qemu (including qemu-system, etc): 1:4.2-3ubuntu6.19
virt-manager: 1:2.2.1-3ubuntu2.1
virt-viewer: 7.0-2build1

Guest software versions:
XOrg X Server: 1.21.1.2
Libinput: 1.19.2.r0

Virt-manager setup includes:
Keyboard: Generic USB keyboard
Tablet: Evtouch USB graphics tablet (absolute movement)
Display: Spice (also tried with VNC)

Any idea how to make X find and accept the tablet pointer?

-Compilebunny