[Lenovo YOGA 3 Pro 1370] trackpad does not work

Ubuntu release: 20.04.2 LTS
Laptop: Lenovo YOGA 3 Pro 1370
Touchpad is unkown, (seemingly?) not listed in /proc/bus/input/devices

Touchpad initially worked upon installation, then stopped working once I used the touchscreen. Now it does not work at all any more; restarts with or without an external mouse doesn't help.

I was directed here from https://wiki.ubuntu.com/DebuggingTouchpadDetection#generalinfo

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: linux-image-5.8.0-43-generic 5.8.0-43.49~20.04.1
ProcVersionSignature: Ubuntu 5.8.0-43.49~20.04.1-generic 5.8.18
Uname: Linux 5.8.0-43-generic x86_64
NonfreeKernelModules: wl
ApportVersion: 2.20.11-0ubuntu27.16
Architecture: amd64
CasperMD5CheckResult: skip
CurrentDesktop: ubuntu:GNOME
Date: Fri Apr 23 10:19:30 2021
InstallationDate: Installed on 2021-04-22 (0 days ago)
InstallationMedia: Ubuntu 20.04.2.0 LTS "Focal Fossa" - Release amd64 (20210209.1)
ProcEnviron:
 TERM=xterm-256color
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=de_DE.UTF-8
 SHELL=/bin/bash
SourcePackage: linux-signed-hwe-5.8
UpgradeStatus: No upgrade log present (probably fresh install)